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Frontispiece. 


Foot  of  Spider,  X  150. 


PRACTICAL 


Photo-Micrography: 


BY  THE  LATEST  METHODS, 


BY 

ANDREW  PRINGLE,  F.R.M.S., 

President  of  the  Photographic  Convention  of  the  United  Kingdom , 
1889.  Joint- Author  of  “ Processes  of  Pure 
Photography  '  etc.,  etc. 


NEW  YORK: 

THE  SCOVILL  &  ADAMS  COMPANY. 
1890. 

C.°  . 

GOT 

2sr 


TO  THE  MEDICAL  PROFESSION, 


THIS  BOOK,  PARTLY  INTENDED  TO  PROMOTE 
PHYSIOLOGICAL  RESEARCH 
BY  PHOTOGRAPHIC  METHODS, 

IS  DEDICATED. 


Copyright,  1890, 

By  The  Scovill  &  Adams  Company. 


THE  GETTY  CENTER 

LIBRARY 


PREFACE. 


No  apology  seems  to  be  necessary  for  this  book.  So  far  as 
I  know,  no  attempt  has  been  made  by  any  person  apparently 
up  in  the  subject  to  give  instructions  for  Photo-micrography, 
since  time  has  elapsed  for  proper  trials  of  the  two  great  and 
novel  features  of  the  Science,  Apochromatic  Objectives  and 
Color-correct  Plates.  My  experience,  though  limited  in  dura¬ 
tion,  has  been  gained  by  assiduity  and  very  varied  practice, 
and  the  whole,  practically,  of  my  study  has  been  directed  to 
the  investigation  and  utilization  of  our  two  new  tools  above 
named. 

I  have  written  deliberately  and  confessedly  for  the  Natural 
and  Medical  Sciences  rather  than  for  those  who  use  the  micro¬ 
scope  as  a  pastime.  But  I  have  not  overlooked  the  intelligent 
investigators  of  such  subjects  as  diatom-structure  and  the  like ; 
for  in  objects  whose  real  structure  is  so  problematic  lies  not 
only  a  valuable  field  for  optical  research,  but  much  of  the 
future  of  practical  optics,  and  perhaps  the  very  best  manege 
for  the  student  photo-micrographer.  I  boast,  however,  to 
have  written  something  that  will  materially  help  those  who 
study  the  Natural  Sciences  in  general  rather  than  Optical 
Science  in  particular. 

I  have  to  thank  many  friends  for  help  of  various  kinds. 
Mr.  Edward  M.  Nelson,  my  instructor  in  practical  microscopy, 
has  placed  me  under  the  most  marked  obligation,  for  he  kindly 
read  my  M.S.  so  far  as  it  touched  optical  theories,  and  he 
directed  me  where  necessary.  I  owe  so  much  generally  to 


4 


PREFACE. 


Dr.  R.  L.  Maddox  that  I  need  not  particularize  any  late  favors. 
I  thank  certain  opticians  for  blocks  which  appear  in  these 
pages,  notably  Mr.  Powell,  Mr.  Swift,  Mr.  Beck,  Mr.  Baker, 
and  Mr.  Newton. 

Apology  is  perhaps  due  for  over  frequent  reference  to  a 
book  in  the  writing  of  which  I  took  part.  It  seemed  better 
to  refer  even  to  my  own  writings  than  to  waste  space  in  the 
present  book. 


Andrew  Pringle. 


CONTENTS 


Preface,  - 
Description  of  Plates, 

CHAPTER  I. 

Introductory  and  Historical,  - 


Preparations  for  Work, 


Optical  Apparatus, 


CHAPTER  II. 


CHAPTER  III. 


CHAPTER  IV. 

Optical  Apparatus  Continued, 


CHAPTER  V. 


Illumination. 


CHAPTER  VI. 

Photo-Micrographic  Apparatus,  .... 

CHAPTER  VII. 

Requisites  for  Photography,  - 

CHAPTER  VIII. 

Solutions  for  Photographic  Operations, 

CHAPTER  IX. 

On  the  Selection  of  Plates,  - 

CHAPTER  X. 

The  Condenser  and  Bull’s-Eye— Their  Use  and  Abuse, 

CHAPTER  XI. 

The  Use  of  the  Eye-Piece  or  Ocular — Stops— Reflections, 

CHAPTER  XII. 

Progressive  Examples,  ..... 


PAGE. 

3 

7-10 


11 

17 

22 

33 

39 

47 

55 

61 

65 

69 

74 

79 


6  CONTENTS. 

CHAPTER  XIII.  page. 

Exposure,  88- 

CHAPTER  XIV. 

Development  of  Gelatine- Bromide  Plates,  -  -  -  91 

CHAPTER  XV. 

Operations  Following  Development,  -  -  -  101 

CHAPTER  XVI. 

Color-Correct  Photography,  -  105 

PART  II. 

Introductory,  -------  113. 

CHAPTER  XVII. 

Printing  on  Albumenized  Paper,  ....  -  115 

CHAPTER  XVIII. 

Gelatine  Chloride  Paper,  -  121 

CHAPTER  XIX. 

Printing  on  Bromide  Paper,  -  123 

CHAPTER  XX. 

The  Platinotype  Process,  .....  130 

CHAPTER  XXI. 

Enlarging,  -  --  --  --  -  134 

CHAPTER  XXII. 

Lantern  Slides,  -------  143 

CHAPTER  XXIII. 

Use  of  the  Optical  Lantern,  -  155 

CHAPTER  XXIV. 

Immersion,  Apochromatics,  and  Aperture.  Oculars,  -  162 

CHAPTER  XXV. 

Classification  of  Objects— How  to  Treat  Them,  -  -  167 

CHAPTER  XXVI. 

Black  Backgrounds.  Opaque  Mounts.  Polarized  Objects,  174 


PLATES. 


Frontispiece. 

Foot  of  Spider,  X  150. 

Color  of  object — Brown-yellow.  Objective — 16  mm.  apochromatie. 

Screen  used — Pale  yellow.  Ocular — Projection  No.  3. 

Condenser — Lower  part  of  achro. 

by  Swift. 

Light — Lime. 

Plate — Landscape  gel.  brom. 
Exposure — 5  minutes. 
Development — Pyro  ammonia. 

Plate  I. 


Critical  image,  X  375. 

Objective  —  6  mm.  apochromatie, 
N.  A.  •  95,  Zeiss. 

Ocular — Projection  No.  3. 
Condenser — Achromatic  140  deg. 
Light — Lime. 

Plate — Lantern-slide  gel.  brom. 
Exposure — 2  minutes. 
Development — Pyro  ammonia. 


Injected  Villi,  Intestine  of  Rabbit,  X  30.  Preparation  by  E.  C.  Bous- 
field,  L.R.C.P. 

Color — Very  dense  orange-yellow.  Objective — Swift  1  inch. 

Screen — None.  Ocular — None. 

Condenser — Lower  part  of  achro. 
with  author’s  ground  glass 
(see  p.  71). 

Plate — Eosin. — Light-Lime. 
Exposure — 14  minutes. 
Development — Pyro  ammonia. 


Hairs  on  Proboscis  of  Blowfly. 
Color  of  image — Brown. 

Screen — None. 


8 


PLATES. 


Plate  II. 

1. 

A.  Margaritaceus,  X  150;  General  appearance. 

Objective — 16  mm.  apo.  at  N.  A.  ‘30. 
Ocular — Projection  No.  3. 
Condenser — Lower  part  of  achro. 
Light — Lime. 

Plate — Thickly  coated  landscape. 
Exposure — 40  seconds. 
Development — Pyro  ammonia. 

2. 

Triceratium.  Critical  image  of  secondary  structure,  X  750. 

Objective — 3  mm.  apo.  at  N.A.  1. 
Ocular  — Projection  No.  3. 
Condenser — Powell  and  Lealand 
used  dry. 

Light — Lime. 

Plate — Thickly  coated  landscape. 
Exposure — 45  seconds. 
Development — Pyro  ammonia. 


Plate  III. 


l. 


“Taste-buds  ”  in  Tongue.  X  100.  Preparation  by  E.  Klein,  M.D.,  F.R.S. 
Stain — Logwood.  Objective — 24  mm.  apo.  Zeiss. 

Screen — Pale  yellow.  Ocular — Projection  No.  3. 

Condenser — Achro.  lower  part, 

with  author's  ground  glass. 

Light — Lime. 

Plate — Eosin. 

Exposure — 15  seconds. 
Development — Pyro  ammonia. 

2. 


•Typhoid  bacilli  in  Intestine.  X  750.  Preparation  from  the  Research 
Laboratory,  Royal  College  of  Physicians,  Edinburgh. 

Stain — Gentian  violet.  Objective — 3  mm.  apo.  at  about 

Screen — Medium  yellow.  N.A.  1. 

Ocular — Projection  No.  3. 
Condenser — Zeiss.  Apo.  N.A.  1. 
Light—  Lime. 

Plate — Eosin. 

Exposure — 90  seconds. 
Development — Quinol-caustic. 


PLATES. 


9 


Plate  IV. 


B.  Anthracis  in  blood.  X  750. 
Stain — Deep  gentian  violet. 
Screen — Medium  yellow. 


Spermatozoa  of  Triton,  X  1000. 
Stain — F  uchsine. 

Screens — 1  pale,  1  dark,  yellow. 


Preparation  by  W.  T.  Wilson,  V.S 
Objective — 3  mm.  apo. 

Ocular — Projection  No.  3. 
Condenser — Achro.  at  about  140 
deg. 

Light — Lime. 

Plate — azaline  stained. 

Exposure — 35  seconds. 
Development — Pyro  ammonia. 

2. 

Preparation  by  G.  F.  Dowdeswell. 
Objective — 2  mm.  apo. 

Ocular — Projection  3. 

Condenser — Achro.  140  deg. 

Light — Lime. 

Plate — Eosin. 

Exposure — About  2  minutes. 
Development — Pyro  ammonia. 


Plate  V. 


"Pneumococci,”  encapsuled.  x  500. 


Stain — Fuchsii  e-deep. 
Screen — None. 


Objective — oil.  Swift. 

Ocular — none. 

Condenser — Achromatic  140  deg. 
Light — Oil  lamp. 

Plate — Ordinary  rapid, 

Exposure — about  9  minutes. 
Development — Pyro  ammonia. 


2. 

Flagellated  Spirilla  (?  serpens)  x  800. 
Maddox,  M.D. 

Unstained. 

Screen — Medium  yellow. 


Preparation  by  R. 


Objective — 3  mm.  apo. 

Ocular — Projection  No.  3. 
Condenser— Acromatic. 

Light — Lime. 

Plate — Landscape. 

Exposure — 2*4  minutes. 
Development — Pyro  ammonia. 


10 


PLATES. 


Plate  VI. 

1. 

Bacilli  Tuberculosis  in  Lung  of  Horse,  x  750.  Preparation  by  W. 
Watson  Cheyne,  F.R.C.S. 

Stains — Bacilli-red. 

Tissues — Pale-blue  and  yellow. 

Screen — Deep  yellow.  Objective — 3  mm.  apo.  used  at 

N.A.  1. 

Ocular — Projection  No.  3. 
Condenser — Powell  and  Lealand, 
used  dry. 

Light — Lime. 

Plate — “  Isochromatic.” 

Exposure — 2%  minutes. 
Development — Q  u  i  n  o  1  (hydro- 

quinone)  and  caustic  soda. 

2. 

B.  Tuberculosis  by  Inoculation.  Lung  of  Rabbit,  x  600.  Prepara¬ 
tion  by  E.  Klein,  M.D.,  F.R.S. 

Stain — Red  and  blue.  Objective — 3  mm.  apo. 

Screen — Medium  yellow.  Ocular — Projection  No.  3. 

Condenser — N.  A.  I. 

Light — Lime. 

Plate — Eosin. 

Exposure — minute. 

Development — Quinol  caustic. 

The  reader  is  requested  to  note  that  these  illustrations  are  given  not 
as  perfect  specimens  of  work,  nor  as  the  best  that  have  been  produced  by 
the  author  ;  they  are  given  to  illustrate  various  types  of  subjects  and 
varied  treatment. 

Fig.  2  of  Plate  VI.  is  not  a  good  representation  of  the  original  negative. 


Practical  Photo-Micrography. 


CHAPTER  I. 

INTRODUCTORY  AND  HISTORICAL. 

It  would  be  out  of  place  and  inconvenient  for  the  writer 
here  to  enter  into  any  elaborate  apology  for  the  Science  of 
Photo-micrography,  or  to  occupy  useful  space  with  a  lengthy 
discourse  on  the  reasons  that  led  him  to  make  a  study  of  the 
Science.  Any  one  of  a  scientific  turn  of  mind,  and  especially 
one  who  has  more  or  less  mastered  the  science  of  Photography, 
could  not,  on  entering  the  microscopic  world,  fail  to  realize 
how  great  a  boon  Photography  might  become  to  microscopy, 
if  the  photographer  were  a  good  microscopist  and  the  micro- 
scopist  a  skilled  photographer.  Should  the  world  ever  possess 
in  one  man  a  skilled  and  careful  microscopist  and  an  experi¬ 
enced  and  versatile  photographer,  a  very  great  step  may  be 
expected  not  only  towards  solutions  of  many  present  enigmas 
and  towards  future  discoveries,  but  also  towards  a  very  satis¬ 
factory  and  very  convincing  medium  for  publishing  and  cer¬ 
tifying  the  solutions  and  discoveries. 

The  potential  value  of  Photography  in  this  line  has  always 
been  admitted  and  often  dwelt  upon;  but  difficulties,  some 
real,  some  exaggerated,  some  imaginary,  have  always  been  cited 
as  fatal  to  the  employment  of  Photography  for  the  delineation 


12 


PRACTICAL  PHOTOMICROGRAPHY. 


by  a  graphic  method  of  microscopic  images.  That  difficulties, 
and  often  great  ones,  present  themselves  is  matter  of  fact,  but 
to  smooth  over  some  of  these  difficulties,  to  evade  some  and 
to  conquer  others,  it  is  the  writer’s  ambition  to  assist  the 
reader. 

Two  classes  of  photo-micrographer  are  met  with  in  the 
ordinary  course ;  the  first  a  microscopist  of  more  or  less  ex¬ 
perience  and  skill,  who  suddenly  bethinks  himself  that  photog¬ 
raphy  seems  an  easy  and  rapid  way  of  graphically  represent¬ 
ing  his  objects  and  his  observations ;  he  never  doubts  that  he 
may  in  a  very  short  time  master  the  elementary  troubles  of 
photography,  and  accordingly  he  embarks  in  a  cockle-shell  on 
the  most  stormy  waves  of  a  great  and  growing  science.  The 
other  class  of  photo-micrographer  is  the  photographer,  usually 
the  amateur,  who  thinks  he  has  conquered  the  realms  of  land¬ 
scape  and  portraiture,  and  sighs  only  for  fresh  conquests ;  and 
so  he  plunges  blindly  into  the  science  which  of  all  others  re¬ 
quires  practice,  perseverence  and  acute  powers  of  observation. 
The  results  are  shame  and  calamity  to  photo-micrography 
as  a  utility,  as  an  educator,  as  a  science.  Photo-micrography 
has  not  yet  taken  the  place  it  deserves,  demands,  and  shall 
finally  take.  It  is  much  to  be  regretted,  but  it  is  true,  that  we 
have  so  many  books  on  photo-micrography  written  by  men 
who  are  only  smatterers  in  microscopy  and  totally  ignorant  of 
anything  but  the  very  rudiments  of  photography.  Much  has 
been  well  written  on  the  subject,  but  the  science  is  advancing 
so  rapidly  that  what  was  in  the  front  one  week  is  “  exploded  ” 
and  improved  out  of  knowledge  the  next  week. 

Even  were  it  desirable,  our  space  makes  it  impossible,  to 
enter  at  any  length  on  the  history  of  photo-micrography.  Some 
assign  the  credit  of  the  first  photo-micrograph  to  one  person, 
some  to  another;  but  we  confine  ourselves  to  saying  that 
among  the  earliest  workers  in  this  line  were  Wedge  wood,  Rev. 
J.  B.  Reade  (about  1837),  Mr.  Dancer  (1840),  Mons.  Donne 
(1840),  Mr.  Archer  (1851),  etc.  Among  the  early  workers 
was  Dr.  R.  L.  Maddox,  admittedly  the  suggestor  of  gelatine 
emulsion  for  photography,  and  still  alive  to  view  the  results 
of  his  own  work  and  talents,  and  to  lend  a  helping  hand  and 


PRACTICAL  PHOTO-MICROGRAPHY. 


13 


give  valuable  instruction  to  beginners  as  he  most  generously 
did  to  the  writer.  No  man  has  worked  more  perseveringly  or 
more  successfully  in  this  branch  of  science  than  Dr.  Maddox, 
and  no  man  ever  got  less  reward — beyond  that  of  conscious 
merit — than  our  good  friend.  His  photographs  of  Pleuro- 
sigma  angulatvm  X  3,000,  of  many  micro-organisms,  and  of 
various  other  subjects  still  rank  among  the  best  works  that 
have  been  produced. 

The  work  of  Dr.  Woodward  of  the  U.  S.  Army  was  so  re¬ 
markable  and  so  excellent  as  to  mark,  or  even  to  make ,  an  era 
of  itself.  This  scientist  was  a  microscopist  of  the  very  fore¬ 
most  rank,  a  generous  government  placed  at  his  disposal 
the  very  best  instruments,  and  the  results  amply  justified  the 
country’s  confidence,  for  Dr.  Woodward’s  photo-micrographs 
of  Arnjjhipleura  pellucida ,  of  Nobert’s  test  plates,  of  the 
well-known  test  “  Podura  scales,”  as  well  as  of  many  physio¬ 
logical  and  pathological  subjects  have  seldom  if  ever  been 
equalled.  If  these  works  of  Dr.  Woodward’s  are  ever  beaten 
the  superiority  will  be  due  to  late  improvements  in  optical  ap¬ 
pliances,  and  to  the  use  of  more  sensitive  “  color-correct  ”  plates 
for  photography. 

Dr.  Koch,  the  eminent  authority  on  micro-organisms,  has 
produced  fine  photographs  of  bacteria,  and  Dr.  E.  M.  Crook- 
shank,  Professor  of  Bacteriology  at  King’s  College,  London, 
has  published  not  only  a  number  of  photographs  of  Bacteria 
but  also,  in  a  succinct  and  ably  written  book,  his  methods  of 
producing  his  photographs  with  capital  diagrams  of  his  ap¬ 
paratus.* 

The  Diatomacese,  as  might  be  expected  from  their  beauty, 
have  always  been  favorites  with  the  photo-micrographer,  but 
from  their  formation  they  have  always  proved  severe  tests  for 
the  powers  of  those  who  have  attempted  them.  Besides  the 
micrographs  of  Dr.  Woodward  we  must  notice  some  very  fine 
work  by  Dr.  Mercer,  also  an  American  citizen.  Drs.  Aber¬ 
crombie  and  Wilson  in  England  were  very  successful  in  photo¬ 
graphing  the  diatomaceae,  and  lately  Messrs.  A.  Truan  y  Luard 

*  Photography  of  Bacteria,  by  Edgar  M.  Crookshank,  M.  B.,  F.  R.  M.  S. 
London :  H.  K.  Lewis.  1887. 


14 


PRACTICAL  PHOTO-MICROGRAPHY. 


and  Otto  1ST.  Witt,  the  former  of  Spain,  the  latter  of  Prussia, 
have  succeeded  in  producing  a  magnificent  set  of  photographs 
of  the  Diatomaceae  of  Hayti,  West  Indies.  These  collabora- 
teurs  found  that  they  obtained  the  best  results,  or  rather  the 
only  good  results,  by  using  the  wet  collodion  process.  The 
writer,  while  inclined  to  traverse  this  assertion  of  the  superior¬ 
ity  of  wet  collodion  over  suitable  gelatine  emulsion,  will  have 
occasion  to  advert  to  the  modus  operandi  of  these  undoubtedly 
skillful  and  successful  workers  in  a  later  part  of  this  book. 
Dr.  R.  Zeiss,  of  J ena,  has  lately  exhibited  certain  photographs 
of  A.  Pellucida  and  P.  Angulatum ,  which  in  Britain  excited 
considerable  comment  of  a  highly  favorable  kind.  The  late 
Isaac  H.  Jennings  produced  some  very  creditable  photographs 
of  diatoms,  notably  one  of  N.  Lyra /  and  his  treatise  on  Photo¬ 
micrography  is  one  of  the  best  in  the  English  language, 
though  late  optical  and  photographic  advances  have  made  the 
book  a  little  out  of  date.*  Another  work  worthy  of  perusal, 
on  account  of  the  careful  treatment  in  brief  space  of  the  opti¬ 
cal  part  of  the  subject,  is  that  by  Dr.  E.  C.  Bousfield,  who  is 
not  only  an  adept  with  the  microscope  but  has  been  highly 
successful  in  the  department  of  photo-micrography,  f 

Still  confining  himself  to  work  that  he  has  seen,  the  writer 
would  now  draw  attention  to  the  magnificent  “  critical  image- 
photographs”  of  Mr.  E.  M.  Nelson, of  London.  A  microscop- 
ist  of  long  and  varied  practice,  of  consummate  skill,  and  pos¬ 
sessed  of  an  intimate  knowledge  of  microscopic  optics,  Mr. 
Nelson  has  laid  himself  out  for  the  most  difficult  branches  of 
photo-micrography,  the  photography  of  the  highest  possible 
resolutions  of  such  subjects  as  muscle-fibrils,  “  secondary  struc¬ 
ture  ”  of  the  diatomaceae,  and  ordinary  diatom  structure  of  the 
most  delicate  kind.  To  Mr.  Nelson  the  writer  owes  practi¬ 
cally  all  the  knowledge  he  has  of  microscope-manipulation, 
and  to  Mr.  Nelson’s  unstinted  instruction  and  careful  explana¬ 
tions  the  writer  is  indebted  for  any  measure  of  success  lie  has 

*  Photo-micrography ;  or,  How  to  Photograph  Microscopic  Objects. 
By  I.  H.  Jennings.  London:  Piper  &  Carter.  1886. 

f  Guide  to  the  Science  of  Photo-micrography.  By  Edward  C.  Bousfield, 
L.  R.  C.  P.  London  :  W.  Kent  &  Co.  1887. 


PRACTICAL  PHOTO-MICROGRAPHY. 


15 

had  in  this  branch  of  science ;  not  forgetting  the  unwearying 
kindness  of  Dr.  Maddox  when  the  writer  was  an  entire  novice 
in  everything  microscopic. 

A  great  many  other  names  would  have  to  be  mentioned  did 
this  chapter  profess  to  be  a  history  of  the  science  with  which 
we  are  dealing.  Drs.  Draper  and  Sternberg  of  America  have 
done  more  than  “Yeoman  Service  ”  in  this  line;  Mr.  Wen- 
ham,  Mr.  T.  Charters  White,  Mr.  Shadbolt,  Dr.  Lionel  Beale  in 
England ;  in  France  Dr.  Miquel  and  others ;  in  Italy  Count 
Abbe  Castracane ;  and  ISTeyt  in  Belgium — all  have  made  their 
marks  in  photo-micrography.  Dr.  Heneage  Gibbes,  now  Pro¬ 
fessor  of  Physiology  in  Michigan,  and  Mr.  F.  EL  Evans,  of 
London,  have  produced  some  useful  photographs  of  physio¬ 
logical  preparations.  So  of  late  years  have  many  other  per¬ 
sons,  for  the  value  of  photography  in  this  line  is  daily  attract¬ 
ing  more  and  more  attention.  It  appears  to  the  writer  that 
for  the  instruction  of  a  class  of  students  in  such  branches  as 
histology,  physiology,  pathology,  bacteriology,  etc.,  no  method 
can  equal  the  use  of  an  Optical-lantern  slide  projected  upon  a 
screen,  the  room  being  temporarily  darkened ;  there  are  no 
such  difficulties  or  inconveniences  as  would  at  first  sight  ap¬ 
pear,  and  a  chapter  of  this  book  shall  be  devoted  to  the  sub¬ 
ject,  in  the  hope  that  attention  may  be  called  to  this  very 
scientific  and  convenient  means  of  imparting  instruction. 

A  few  words  may  aptly  be  written  on  what  the  writer 
claims  as  the  advantages  of  photo-micrography  over  other  ex¬ 
isting  methods  of  delineation.  In  the  first  place,  “  Personal 
Equation,”  or  perhaps  “Personal  Prejudice,”  is  almost  entirely 
eliminated.  A  dishonest  man  may  possibly  arrange  his  pho¬ 
tography  so  as  to  bear  out  his  own  previous  assertions,  but  a 
candid  person  doing  his  best  to  secure  truth  will  be  confident  * 
that  what  his  photograph  shows  represents  what  his  lens 
“  saw,”  and  those  who  see  his  photograph  will  know  that  it  re¬ 
presents  the  object  in  one  aspect  at  least.  The  aspect  may  be 
a  delusive  one  through  optical  mismanagement,  but  it  must  be 
one  aspect  of  the  object.  Photography  certainly  cannot  lie, 
but  the  photographer  may  be  a  liar  or  a  fool.  For  this  reason 
the  photo-micrographer  must  not  only  be  unprejudiced  and 
honest,  he  must  also  be  a  microscopist  and  know  his  object. 


16 


PRACTICAL  PHOTOMICROGRAPHY. 


Many  microscopic  objects  are  so  fine  in  substance,  others  so 
intricate  in  structure,  that  the  human  hand  is  unable  by  any 
device  to  draw  them  anything  like  accurately.  No  line  visible 
to  the  naked  eye  is  too  fine  for  photography  to  limn,  no  struc¬ 
ture  too  intricate  for  the  pencil  of  light  to  follow. 

By  photo-micrography  a  vast  amount  of  time  is  saved.  A 
few  minutes  of  work  may  furnish  us  with  a  matrix  for  a 
thousand  prints,  one  of  which,  if  possible  at  all,  could  not  be 
produced  by  hand  in  many  hours.  By  photography  are  done 
with  moderate  ease  and  complete  accuracy  many  subjects  which 
by  hand  could  not  be  done  at  all,  witness  moving  objects,  and 
appearances  rapidly  changing. 

Many  other  claims  might  be  made  for  photo-micrography, 
but  we  shall  cite  only  one  more.  Of  all  the  intellectual  and 
scientific  pursuits  that  can  be  named,  no  one  possesses  so  great, 
so  varied  fascinations  as  photo-micrography.  There  is  mental 
food  and  mental  exercises  for  every  one ;  microscopy  in  all 
its  varied  branches  and  with  all  its  interests — optics,  mechanics, 
chemistry ;  and  best  of  all,  a  practical,  visible,  permanent,  use¬ 
ful  result — an  education  and  an  educator ! 

Note. — Since  the  above  was  written,  Drs.  Fraenkel  and  Pfeiffer,  of 
Berlin,  have  begun  to  publish  a  set  of  photo-micrographs  of  bacteria 
which  may  be  called  splendid.  They  use  daylight,  apochromatic  lenses 
and  orthochromatic  plates. 


CHAPTEK  II. 


PREPARATIONS  FOR  WORK. 

A  great  deal  of  time,  trouble  and  expense  will  be  saved  by 
a  careful  consideration  of  certain  matters  before  any  attempt  is 
made  at  actual  work.  It  is  probable  that  after  actual  work 
has  been  carried  on  for  some  time  alterations  may  be  found 
necessary  and  improvements  may  suggest  themselves ;  but  the 
earlier .  lessons  of  practice  and  experience  will  be  well  nigh 
wasted  if  there  is  not  in  the  first  arrangements  a  certain  amount 
of  forethought  and  fore-knowledge.  We  shall  here,  therefore, 
endeavor  to  smoothe  the  way  for  the  beginner  by  giving  hints, 
as  close  as  possible  to  directions,  on  such  matters  as  apartments, 
and  apparatus  of  a  general  nature,  leaving  a  more  detailed  de¬ 
scription  of  special  apparatus  for  future  chapters. 

A  great  advantage  will  arise  from  having  two  apartments 
communicating  with  each  other  for  the  two  branches  of  the 
work  :  the  microscopic  or  exposure  work,  and  the  photographic 
nr  development  work.  If  two  communicating  apartments  are 
not  available,  two  adjacent  ones  may  do  almost  as  well ;  or 
with  certain  evident  precautions  one  chamber  may  be  used  for 
both  lines  of  operation.  Wherever  the  apartment  for  making 
the  exposure  may  be,  it  is  of  the  utmost  importance  that  it  be 
steady ;  with  a  good  sound  floor,  and  as  far  as  possible  removed 
from  house  or  street  traffic.  No  place  is  usually  so  suitable  as 
a  basement  or  half-basement  cellar,  and  if  this  ground  apart¬ 
ment  have  floor  and  walls  of  cement,  and  a  strong  ceiling,  it 
will  probably  be  perfectly  adapted  for  the  work.  But  even 
such  an  apartment  should  be  as  far  as  possible  distant  from 
street  traffic,  if  the  finest  photo-micrographic  work  is  intended. 
Mr.  E.  M.  Nelson,  alluded  to  in  last  chapter,  works  in  a  cellar 
such  as  just  described,  using  for  his  apparatus  a  base  not  only 
itself  very  heavy  but  further  weighted  with  several  hundred- 


18 


PRACTICAL  PHOTOMICROGRAPHY. 


weight  of  lead,  yet  he  never  attempts  his  most  critical  work 
till  after  9  p.  m.,  though  he  does  not  live  in  a  very  busy  thor¬ 
oughfare  but  in  a  quiet  suburb  of  London.  The  writer,  too, 
works  in  a  cement-floored  and  walled  lialf-basement  in  a  very 
quiet  village,  but  has  had  negatives  spoiled  by  the  tremor  of  a 
passing  ’bus  or  of  a  heavy  step  overhead.  There  should  be  no 
chance,  therefore,  of  vibration  or  tremor  in  any  part  of  the 
apparatus  or  apartment.  And  further,  the  whole  of  the  appar¬ 
atus  actually  used  to  produce  a  negative — the  light,  the  con¬ 
denser-system,  the  microscope,  the  camera  and  the  plateholder 
— should  all,  during  exposure  at  least,  be  practically  one  solid 
mass ;  in  other  words,  the  whole  system  must  be  firmly 
clamped  to  one  base,  and  that  base  should  be  the  floor  if  pos¬ 
sible.  The  entire  system  being  clamped  to  one  base,  even 
if  that  base  be  not  itself  above  suspicion,  moving,  all 
other  parts  move  in  unison,  so  that  blurring  may  be 
avoided ;  we  have  heard  of  a  plan  by  no  means  bad, 
wherein  the  whole  system  on  a  strong  base  was  suspended  by 
cords  from  a  high  support.  If  strong  India-rubber  formed  part 
of  the  length  of  these  cords  the  apparatus  was  probably  very 
satisfactory,  and  the  idea  was  surely  ingenious.  India-rubber 
cubes  have  often  been  found  very  beneficial  as  supports  for 
the  base-board  of  a  system  where  tremor  is  inevitable. 

If  by  any  chance  the  illuminant  to  be  used  is  daylight, 
whether  diffused  or  direct  sunlight,  this  consideration  must 
naturally  play  an  important  part  in  the  selection  of  an  apart¬ 
ment.  If  daylight  is  to  be  used  for  the  development  of  the 
photographic  plates,  a  course  which  we  do  not  recommend,  it 
is  almost  essential  that  the  window  of  the  room  chosen  face 
the  North.  The  writer  has  but  little  experience  of  daylight 
as  the  illuminant  for  making  the  exposure  in  the  camera,  but 
where  daylight,  and  especially  sunlight,  can  be  depended  on, 
it  is  perhaps  the  best  of  all  illuminating  agents.  In  Britain 
we  believe  it  impossible  to  obtain  anything  like  uniform  re¬ 
sults,  though  no  doubt  at  odd  times  great  successes  may  be, 
and  have  been,  scored  by  sunlight.  Now  that  photographic 
emulsions  are  made  so  sensitive  to  actinic  light,  the  great  ad¬ 
vantage  of  sunlight  is  of  les3  consideration,  while  the  superior 


PRACTICAL  PHOTO-MICROGRAPHY. 


19 


equability  of  artificial  light  makes  it  a  far  more  certain  factor 
in  our  work  than  ever  daylight  could  be,  even  at  its  best  and 
steadiest.  The  fact  that  some  magnificent  work — as  of  Drs. 
Woodward,  Maddox  and  others — has  been  produced  by  daylight 
only  leads  us  to  regret  that  these  eminent  workers  had  not  the 
advantages  we  have  of  equable  radiants  and  very  sensitive 
plates.  There  are,  however,  over  and  above  the  actinic  value 
of  daylight,  certain  qualities  in  daylight  that  make  it,  in  spite 
of  its  inferiority  in  some  respects,  invaluable  if  not  essential 
for  certain  kinds  of  work,  and  we  do  not  wish  to  be  taken  as 
despising  or  rejecting  daylight  entirely  as  our  radiant.  No 
treatise  on  this  subject  would  be  complete  without  more  than 
a  passing  allusion  to  the  use  of  natural  light  as  the  radiant,  and 
accordingly  the  subject  shall  be  treated  in  such  manner  as  is 
within  our  power. 

Another  advantage  worthy  of  note,  though  always  over¬ 
looked,  pertaining  to  basement  apartments,  is  the  equability 
of  temperature.  The  writer’s  half-basement  operating  rooms 
do  not  vary  10  deg.  Falir.  in  the  course  of  the  entire  year ; 
never  unbearably  cold  in  winter  they  are  a  refreshing  change 
from  the  outside  heat  of  summer.  This  is  of  more  importance 
to  the  advanced  photo-micrograplier  than  might  appear ;  the 
microscopic  apparatus  keeps  better  and  works  better  in  such 
conditions,  and  in  such  a  room,  in  cold  weather  especially.  The 
heat  arising  from  the  radiant  of  whatever  kind  it  be,  pro¬ 
duces  much  less  serious  effects  on  the  apparatus,  and  much 
less  time  is  required  for  the  parts  to  “  settle  ”  into  their  places. 
(Seep.  173.) 

The  above  remarks  are  intended  for  those  who  propose  to 
enter  seriously  into  the  work  of  photo-micrography.  Those 
who  propose  only  to  work  at  odd  times  or  on  the  easier  sub¬ 
jects,  will  not  require  such  perfect  preparations,  or  such  per¬ 
fectly  adapted  apartments ;  it  will  be  well,  however,  for  every 
intending  worker  to  keep  our  hints  in  mind  and  to  choose 
apartments  as  nearly  as  possible  fulfilling  our  desiderata. 

The  purely  photographic  exigencies  of  the  work  may  be 
met  either  completely  or  partially  according  to  the  means  and 
intentions  of  the  worker.  Development  of  a  micrographic 


20 


PRACTICAL  PHOTO-MICROGRAPHY. 


negative  is  a  matter  requiring  most  accurate  visual  observation, 
and  that  by  a  non-actinic  light ;  the  light  in  question  must 
therefore  be  equable,  ample,  and  “  safe.”  Running  water  is 
so  great  a  convenience  that  many  other  desirables  should,  if 
necessary,  be  sacrificed  for  a  supply  of  water  from  a  tap  ;  for 
this  reason,  and  also  by  reason  of  the  waste-pipe,  we  might  pre¬ 
fer  a  room  otherwise  inconvenient  if  furnished  with  a  tap,  sink 
and  waste-pipe,  to  an  apartment  in  other  respects  more  com¬ 
fortable  and  convenient. 

Critical  photo-micrography  requires  at  every  stage  com¬ 
plete  concentration  of  thought.  The  worker  must  not  be  dis¬ 
tracted  in  the  very  slightest  degree  while  “  setting  up  ”  his 
object  or  while  developing  his  negatives.  All  steps,  therefore, 
should  be  taken  to  avoid  confusion  in  the  rooms  of  work.  The 
fewer  the  bottles  of  chemicals  in  the  dark  room,  and  the  more 
neatly  they  are  arranged  the  better ;  presses  and  shelves  should 
be  provided  for  everthing  required,  which  luckily  is  not  much 
unless  great  digressions  are  to  be  made  from  the  matter  treated 
of  in  this  book. 

Yery  good  work  may  be  done  with  apparatus  of  ordinary 
quality,  but  the  very  best  work  will  only  be  done,  and  can  only 
be  expected  to  be  done,  by  the  very  best  apparatus  used  with 
the  utmost  skill.  We  therefore  counsel  our  Reader  to  begin 
with  the  best  of  everything,  so  far  as  he  can  afford  to  pro¬ 
cure  it.  It  is  false  economy  to  buy  mediocre  instruments 
for  a  start,  because  if  we  succeed  and  persevere  we  are  sure  to 
require  better  implements  as  we  advance  in  skill;  while  if 
we  fail,  become  disheartened,  and  “  chuck  the  thing  up,” 
our  shoddy  outfit  is  valueless. 

It  is  difficult  to  draw  aline  between  “  easy  ”  and  “  difficult  ” 
photo-micrography,  because  each  branch  has  its  own  difficulties. 
In  low-power  work  which  is  often  called  “  easy”  we  have  to 
meet  difficulties  of  uneven  illumination,  uneven  surfaces  and 
puzzling  colors  ;  in  high-power  or  wide  angle  work,  we  have 
to  contend  with  difficulties  in  optics,  in  vibration,  and  in  photo¬ 
graphic  technique.  But  always  the  best  instruments  produce 
the  best  work,  though  often  the  best  instruments  are  the  most 
difficult  to  work  to  their  best  advantage. 


PRACTICAL  PHOTO-MICROGRAPH?. 


21 


If  it  is  true,  and  we  assert  that  it  is  so,  that  the  first  neces¬ 
sity  is  a  knowledge  of  the  use  of  the  microscope  on  our  special 
object,  it  is  no  less  true  that  he  who  begins  photo-micrography 
without  considerable  experience  in  photography  will  have  a 
hard  task  and  many  failures.  The  writer  ventures  to  assert 
that  an  enormous  deal  of  trouble  and  perplexity  will  be  spared 
to  the  tyro  plioto-micrographer  if  he  practise  carefully  before¬ 
hand  ordinary  photography,  specially  of  varied  subjects,  as 
Landscape,  Interior,  Portrait,  and  most  of  all,  Reproduction  of 
colored  objects,  as  Paintings.  The  greatest  stress  will  in  this 
book  be  put  on  color-correct,  or  “  Ortho-Chromatic  ”  photo¬ 
graphy,  because  the  writer  is  well  assured  that  not  only  has 
color-correct  photography  brought  about  vast  improvements  of 
late  in  photo-micrography,  but  that  color-correct  photography 
is  destined  to  be  the  means  of  placing  our  science  in  the  posi¬ 
tion  which  it  claims,  and  will  sooner  or  later  hold  as  the  means 
for  the  delineation  of  microscopic  images.  In  a  book  of  Pure 
Photography,  wherein  the  present  author  had  the  advantage 
of  collaboration  with  Professor  W.  K.  Burton,  C.  E.,  the 
writers  have  pointed  ou  t  with  considerable  clearness  the  effect 
of  variations  in  Exposure  and  Development  in  ordinary  photo¬ 
graphy,  and  the  Reader  is  strongly  recommended  to  study  this 
book,  and  to  gain  as  much  proficiency  as  possible  in  pure  photo¬ 
graphy  before  starting  on  the  special,  but  varied,  operations 
required  to  produce  good  micrographic  negatives  and  prints.* 
The  present  book  will,  however,  treat  photography  on  the 
supposition  of  total  ignorance  on  the  Reader’s  part.  The  same 
course  cannot  be  followed  regarding  the  microscopic  branch  of 
the  subject,  for  this  matter  is  one  of  experience  and  long  and 
close  observation  rather  than  one  which  can,  by  however  much 
writing,  be  imparted  from  writer  to  reader. 


*  The  Processes  of  Pure  Photography,  by  W.  K.  Burton,  C.E,.  and 
Andrew  Pringle,  F.R.M.S.  New  York,  The  Scovill  and  Adams  Co.,  1888. 


CHAPTER  III. 


OPTICAL  APPARATUS. 

Most  of  our  readers  are  pretty  sure  to  possess  a  microscope, 
some  objectives,  eye-pieces,  a  substage  condenser  and  a  bull’s- 
eye.  (Note  :  The  term  condenser  shall  hereafter  be  used  as 
applying  solely  to  the  “  substage  condenser while  “  bull’s-eye  ” 
shall  be  used  to  cover  all  condensing  or  parallelizing  instru¬ 
ments  used  between  condenser  and  light).  Some  kind  of  so- 
called  microscopic  lamp  is  also  likely  to  form  part  of  the  out¬ 
fit.  As  a  rule  a  microscopic  lamp  not  made  specially  for 
microscopy  is  for  various  reasons  unsuited  to  our  purpose. 
Such  adjuncts  to  a  microscope  as  a  Polariser,  a  Paraboloid,  a 
Spot  lens  or  other  arrangement  for  “  black  ground  illumina¬ 
tion  ”  shall  be  treated  separately  ;  till  further  notice  we  shall 
treat  of  axial  transmitted  light  illumination  only. 

The  Microscope.  The  qualities  essential  to  a  microscope- 
stand  for  our  purpose  are  perfect  rigidity,  accurate  working 
of  all  parts,  specially  racks,  fine  adjustments,  stage  mechan¬ 
ism,  and  draw  tubes,  if  any  are  to  be  used.  The  substage  ar¬ 
rangements  as  to  focusing  and  centering  are  just  as  important 
as  the  other  parts  of  the  instrument.  The  writer  proposes  to 
lay  great  stress  on  the  accurate  use  of  the  condenser,  which  is 
often  treated  in  a  careless  and  ignorant  way,  and  sometimes 
even  by  certain  authorities  omitted  altogether.  When  the  func¬ 
tions  of  a  condenser  properly  used  are  explained,  it  will  be 
seen  how  serious  an  omission  this  is.  All  the  best  photo¬ 
micrographic  apparatus  we  have  ever  seen,  and  all  of  which  we 
have  seen  illustrations  that  gave  any  promise  of  excellence, 
have  been  used  on  the  horizontal ;  on  the  other  hand  there  are 
cases  where  the  vertical  position  of  the  apparatus,  i.  e .,  the 
horizontal  position  of  the  stage,  is  necessary.  No  microscope- 
stand  will  meet  both  conditions  unless  it  swing  on  a  pivot, 


Fig.  1 


24 


PRACTICAL  PHOTO-MICROGRAPHY. 


which  pivot  should  be  so  arranged  with  the  working  part  of 
the  swing  that  the  microscope  shall  be  steady  at  whatever 
angle  from  vertical  to  horizontal  it  is  placed.  At  true 
horizontality  the  tube  should  be  stopped  by  a  “  stop  ”  for  the 
purpose.  The  body-tube  of  a  stand  for  our  work  can  hardly 
be  too  wide  in  diameter  so  long  as  we  do  not  reach  the  point 
of  inconvenience  in  adapting  eye-pieces,  etc.,  to  the  tube. 

The  finest  stands  made,  so  far  as  the  writer  knows,  are  those 
of  Powell  &  Lealand,  of  London ;  they  are  perfect  in  rigidity, 
in  mechanism,  in  workmanship  and  finish,  and,  though  expen¬ 
sive,  their  owners  say  they  are  cheap  in  the  long  run. 

A  very  good  stand  is  the  “  Wales”  pattern  of  Messrs.  Swift 
and  Son,  London.  (Fig.  2.)  The  advantage  of  this  form  of 
swing  is  that  the  centre  of  gravity  is  in  the  same  position,  and 
that  a  good  one,  to  whatever  angle  the  tube  is  swung.  The 
writer  used  this  stand  for  high  power  work  with  complete 
satisfaction,  and  that  he  gave  it  up  was  due  not  to  the  stand 
itself,  but  to  certain  exigencies  which  arose  and  could  not  be  met 
with  the  then  arrangement  whereof  this  stand  formed  a  part. 
Consequently  this  stand  is  highly  recommended  to  those  who 
desire  a  good  stand  for  our  purpose  at  a  very  moderate  price 
considering  the  work,  and  the  efficiency.  For  simple  examina¬ 
tion  of  objects,  this  stand  fitted  with  a  Differential  Screw  Fine 
Adjustment,  is  a  most  satisfactory  instrument  for  any  kind  of 
work. 

Beck’s  Stands,  which  are  easily  procurable  in  America,  are 
probably  in  no  way  inferior  to  others,  but  we  cannot  speak 
from  personal  experience. 

A  most  excellent  stand  is  the  one  now  exclusively  used  by 
the  writer  for  photo-micrography.  In  general  the  stand  is  the 
so-called  “  Nelson  ”  pattern,  and  the  one  in  question  was  made 
by  Mr.  C.  Baker,  of  London,  specially  for  the  writer.  This 
stand  was  made  extra  heavy  and  strong  in  all  parts,  with  a 
differential-screw  fine  adjustment  most  accurately  fashioned, 
and  there  is  a  similar  fine  adjustment  to  the  sub-stage.  A 
very  important  feature  not  often  attended  to  in  stands  of 
modest  pretensions,  is  the  rack  work  draw-tube  for  the  cor¬ 
rection  of  objectives  not  furnished  with  “  correction  collars,” 


25 


PRACTICAL  PHOTO-MICROGRAPHY, 

or  with  insufficient  range  of  collar  correction.  In  critical 
work  with  certain  objectives  this  draw-tube  is  an  absolute 


pIG>  2. — Swift’s  Wales  Stand. 


necessity,  and  the  purchaser  of  a  new  outfit  is  recom  mended 
to  insist  on  a  racking  draw-tuhe,  which  will  be  found  conven- 
lent  in  all  cases,  essential  in  some. 


26 


PRACTICAL  PHOTO-MICROGRAPHY. 


These  are  the  stands  of  which  we  have  some  experience  or 
knowledge,  but  there  are  doubtless  other  stands  well  adapted 
to  our  purpose.  Many  of  the  so-called  Students’  Stands  are 
well  and  strongly  made,  their  low  price  being  due  not  so  much 
to  want  of  good  material  and  work  as  to  absence  of  all  delicate 
and  perhaps  unnecessary  mechanism.  In  particular,  the  pat¬ 
tern  of  Hartnack  appears  to  us  commendable  among  cheap  but 


good  microscope  stands.  One  thing,  however,  in  the  cheaper 
class  of  stands  ought  always  to  be  carefully  tested  before  a 
purchase  is  made,  the  jine  adjustment  must  work  true  and 
without  jerk,  deviation  or  “spring and  it  must  be  firm  and  not 
“  give  ”  in  the  slightest  degree  when  the  tube  is  at  any  angle. 
The  long  lever  adjustment  of  Powell  and  Lealand’s  best  stands 
is  considered  the  acme  of  perfection,  and  the  differential 
screw  known  as  “  Campbell’s  ”  is  also  very  trustworthy  when 
well  made.  Mr.  Swift  has  lately  devised  an  additional  inde¬ 
pendent  safety  spring  to  be  used  in  conjunction  with  the 
Campbell  screw  fine  adjustment. 


PRACTICAL  PHOTO-MICROGRAPHY. 


2  7 


Doubtless,  any  well  made  stand  may  be  used  with  complete 
success.  Much  very  fine  work  has  been  produced  with  cheap 
microscopes  not  designed  for  photo-micrograpliy  ;  so  that  any 
one  possessing  any  good  microscope  and  a  moderate  amount  of 
ingenuity  and  neatness  of  hand  need  not  despair  of  success, 
should  his  pocket  not  admit  of  the  purchase  of  a  new  and 
specially  adapted  stand.  One  of  our  diagrams  will  show  how 
easily  any  stand  may  be  used  for  photo-micrography  at  an  odd 
time  or  in  a  casual  way. 

The  Objective,  or  Object  Glass  is,  on  the  whole,  the  most 
important  part  of  the  apparatus.  The  first  essential  is  that 
it  be  “  corrected  for  photography.”*  Objectives  made  for 
ordinary  purposes  of  observation  are  usually  “  over-corrected,” 
a  term  that  requires  explanation.  The  rays  which  give  the 
best  visual  effect  being  less  refrangible  than  those  exercising 
the  greatest  influence  on  chemical  compounds  such  as  we 
employ  in  photography,  the  latter  rays  come  to  focus  behind 
the  focal  point  of  the  visual  rays,  and  naturally  lenses  for 
ocular  observation  only  are  corrected  for  visual  and  not  for 
actinic  rays.  Moreover,  in  order  to  overcome  certain  im¬ 
perfections  of  image  that  would  arise  from  the  interposition 
between  the  object  and  the  lens  of  the  glass  disc  usually 
covering  the  object,  and  also  to  meet  the  fact  that  ordinary 
eye-pieces  are  not  made  achromatic,  the  objectives  are  still 
further  corrected  in  such  a  way  as  still  further  to  separate 
the  visual  from  the  actinic  focus.  The  greater  the  principal 
focus  {i.  e.  the  lower  the  power)  of  the  lens,  the  greater  the 
distance  between  the  foci,  so  that  while  with  a  high 
power  objective  the  foci  may  practically  correspond,  with 
a  low  power  they  are  so  sensibly  separated  as  to  produce  a 
blurred  image  in  photography  while  visually  the  image  was 
quite  sharp.  Of  course,  this  would  be  fatal  to  photo-micro¬ 
graphy.  We  must,  therefore,  either  procure  objectives  cor¬ 
rected  for  photography,  which  is  the  best  plan  by  far,  or 
we  must  by  the  use  of  a  supplementary  lens  so  alter  the 
whole  combination  that  the  visual  and  chemical  ra}rs  shall 

*The  “correction,”  if  not  in  the  objective  itself,  may  be  obtained  by 
use  of  an  ocular  made  for  the  purpose,  Corrections  for  chromatic  and 
spherical  aberations  are,  of  course,  essential  to  all  objectives. 


28 


PRACTICAL  PHOTO-MICROGRAPHY. 


focus  exactly  in  one  plane.  This  supplementary  lens  is 
usually  a  double  convex  fixed  at  the  back  of  the  objective¬ 
cell  ;  it  introduces  extra  reflecting  surfaces  which  should  be 
avoided,  and  it  sensibly  alters  the  focal  length  of  the  objective. 
By  experiment  the  distance  between  the  foci  of  any  lens  may 
be  determined  and  allowance  made  before  each  exposure  by 
withdrawing  the  sensitive  plate  from  the  objective  to  the 
amount  determined  by  the  experiments ;  but  as  the  distance 
differs  not  only  for  each  objective  but  also  for  each  distance 
from  object  at  which  the  objective  is  used,  it  is  plain  that 
such  a  necessity  would  be  an  intolerable  infliction  to  most 
men.  Many,  if  not  all,  opticians  now  produce  objectives  of 
all  powers  most  accurately  corrected  for  the  actinic  rays,  and 
there  is  no  extra  cost  involved.  The  new  apochromatic  object 
glasses  used  with  projection  oculars  are  perfect  in  this  respect, 
and  have  so  many  other  valuable  qualities  that  we  propose  to 
devote  a  chapter,  or  at  least  a  paragraph,  to  them  solely. 

A  much  vexed  question  is  that  of  the  angular  apertures  of 
objectives  not  only  for  photo-micrographic  purposes  but  for 
general  purposes  of  observation.  “  Resolution,”  or  the  power 
of  separating  visibly  line  from  line,  dot  from  dot,  mark  from 
mark,  increases  with  angular  aperture.  Thus  an  objective 
having  an  angular  aperture  of  20  deg.  will,  with  blue  light, 
visibly  separate  lines  about  18,000  to  the  inch,  while  a  lens  of 
120  deg.  will,  under  similar  conditions,  separate  lines  about 
90,000  to  the  inch.  (For  further  remarks  on  angular  aperture, 
immersion,  and  numerical  aperture,  see  Chapter  XXIY, 
pages  162  et  ssq.)  But  as  aperture  increases  certain  useful 
qualities  fall  off.  A  quality  called  “  penetration  ”  is  known  to 
fall  off  in  proportion  as  aperture  increases,  and  this  matter  re¬ 
quires  investigation.  “  Penetration,”  as  it  is  called  in  micro¬ 
scopy,  “  Depth  of  Focus,”  as  it  is  called  in  photography,  is  a 
supposititious  power  of  focusing,  sufficiently  sharply  to  prevent 
visible  blur,  simultaneously  on  several  planes  perpendicular  to 
the  optical  axis  of  the  system.  Plainly  the  essence  of  the  debate 
lies  in  the  amount  of  blur  visible  or  permissible.  In  a  small 
photograph  a  very  small  area  of  confusion  is  permissible,  while 
in  a  larger  photograph  a  comparatively  large  area  of  confusion 


PRACTICAL  PHOTOMICROGRAPHY. 


29 


is  not  only  permissible,  but  preferable  to  over-sharpness 
from  an  artistic  point  of  view.  In  photo-micrography  as  a 
science  we  have  nothing  to  do  with  fine  art,  and  scientifically 
speaking  no  blur  or  confusion-area  is  permissible  at  all.  And 
further  a  lens  cannot  by  any  possibility  focus  equally  sharply 
on  any  two  planes  perpendicular  to  its  axis,  and  any  appear¬ 
ance  of  equal  sharpness  can  only  be  attained  by  a  general  sac¬ 
rifice  of  sharpness,  or  by  a  compromise  between  absolute 
sharpness  on  one  plane  and  absolute  sharpness  on  another 
plane.  When  such  a  compromise  is  made  the  image  may  ap¬ 
pear  sharper  generally,  but  that  is  simply  because  there  being 
no  absolute  sharpness  anywhere  there  is  a  lack  of  sharp  to 
compare  with  unsharp,  and  so  the  eye  is  deceived  into  an  im¬ 
agination  of  sharpness.  And  yet  again  it  is  not  the  case  that 
a  compromising  or  “  diffusing  ”  lens  gives  the  sharpest  image 
as  a  whole,  for  a  lens  capable  of  giving  the  utmost  definition 
on  any  one  plane  will  certainly  show  adjacent  planes  propor¬ 
tionately  sharper  than  the  lens  which  is  incapable  of  giving 
thorough  definition  on  any  plane.  It  is  our  belief  that  this 
misleading  theory  of  penetration,  promulgated  and  upheld  by 
great  authorities  mistaken  on  this  point,  has  done  much  mis¬ 
chief  to  microscopic  optics,  and  led  many  an  optician  and 
many  a  worker  astray.  For  purposes  of  rapid  observation  of 
moving  objects,  where  general  appearances  are  desired  rather 
than  critical  examination,  undoubtedly  low  angle  “  compromis¬ 
ing  ”  lenses  are  of  the  greatest  service,  but  the  writer  ventures 
to  assert,  both  as  a  theory  and  from  careful  and  repeated  ex¬ 
periment,  that  better  photo-micrographs  are  produced,  and  pre¬ 
sumably  better  images  observed,  by  well-made,  wide-angle 
lenses  than  by  lenses  made  for  “  penetration,”  or  stopped  down 
so  as  to  cut  off  available  angle.  Certainly  many  lenses  are 
made  so  imperfectly  that  when  they  are  used  at  their  full 
available  angle  of  aperture  aberrations  come  in  that  spoil  their 
performance  altogether,  but  this  is  a  mechanical  not  a  theo¬ 
retical  fault.  The  writer  regrets  to  say  that  all  this  is  in  flat 
contradiction  to  what  he  wrote  with  reprehensible  precipit¬ 
ancy  when  he  was  but  a  beginner  and  a  “smatterer”  in  this 
science.  But  granting  the  desirability  of  this  quality  of  pene- 


30 


PRACTICAL  PHOTO-MICROGRAPHY. 


tration  there  is  another  matter  to  be  considered.  While  it  is 
true  that  penetration  decreases  in  direct  proportion  as  angular 
aperture  increases,  it  is  also  true  that  penetration  decreases 
much  more  rapidly  as  magnification  increases.  Penetration 
varies  inversely  as  aperture  but  also  inversely  as  the  square 
of  magnification.  So  that  a  low  power  with  a  wide  angular 
aperture  may  be  expected  to  yield  a  better  result  in  the  matter 
of  penetration  than  a  higher  power  with  an  equal  aperture. 
As,  therefore,  aperture  is  the  means  whereby  we  gain  resolu¬ 
tion  and  definition,  and  as  magnification  can  be  obtained  in 
other  ways  than  by  the  use  of  a  high  power  objective,  the  ad¬ 
vantage  clearly  lies  with  the  use  of  a  low  power  of  wide  angle, 
magnification  being  obtained  by  stretch  of  camera,  eye- 
piecing,  or  “  camera  enlargement  ”  of  the  original  negative. 
The  limit  to  the  angular  aperture  of  a  glass  in  proportion  to 
its  focal  length  is  a  difficulty  of  optical  mechanism.  Beyond 
a  certain  point  angular  aperture  in  high  proportion  to  focal 
length  cannot  be  achieved  by  practical  opticians. 

There  is,  however,  one  defect  inseparable  from  the  use  of 
very  wide  angled  objectives,  and  as  it  was  noticed  by  Dr.  Car¬ 
penter  in  his  great  book,  “  The  Microscope  and  its  Revelations  ” 
(London :  Churchill.  Sixth  edition,  1881),  it  may  well  be  put 
in  his  own  words.  After  dwelling  upon  the  difficulty  of  per¬ 
fectly  correcting  a  wide-angled  lens  for  spherical  and  chromatic 
aberrations,  and  after  pointing  out  the  advantages  in  this 
respect  gained  by  the  system  of  homogeneous  immersion,  he 
proceeds  thus :  “  But  here  comes  in  another  source  of  impair¬ 
ment — the  difference  in  the  perspective  views  of  every  object 
not  a  mere  mathematical  point  or  line  which  are  received 
through  the  different  parts  of  the  area  of  the  objective .”  Dr. 
Carpenter  then  quotes  in  support  of  his  position  such  high 
authorities  as  Dr.  Royston  Piggott,  and  Messrs.  Dallinger  and 
Drysdale.  We  might  admit  this  defect  more  readily  if  we 
were  certain  that  “perspective”  can  exist  in  a  diffraction 
image,  but  we  still  believe  that  even  if  Dr.  Carpenter’s  view 
be  correct,  better  results  on  the  whole  will  be  obtained  by  the 
use  of  as  wide  angles  as  can  be  used  without  serious  amounts 
of  aberration. 


PRACTICAL  PHOTO-MICROGRAPHY. 


31 


“  Working  distance  ”  is  also  apt  to  be  curtailed  by  largeness 
of  angle.  “  Working  distance  ”  is  simply  the  distance  between 
the  object  and  the  front  combination  of  the  objective.  With 
low  powers  this  is  of  little  moment,  but  where  we  come  to  use 
high  power  objectives  their  performance  is  not  only  apt  to  be 
impaired  by  very  close  working,  but  there  is  a  danger  of  dam¬ 
age  to  object  or  objective  itself.  Homogeneous  immersion 
helps  us  out  of  the  trouble  to  some  extent,  but  with  cheap 
immersion  lenses  of  numerical  aperture  1.25  and  over,  we  have 
repeatedly  failed  to  observe  objects  that  happened  to  have 
cover  glasses  thicker  than  usual. 

The  “power”  of  an  objective  is  frequently  very  loosely 
quoted.  “Power”  depends  on  focal  length,  and  the  focal 
length  of  a  compound  lens  is  usually  quoted  by  a  supposititious 
comparison  with  a  single  lens  of  given  construction.  The  real 
focal  length  of  an  objective,  and  consequently  its  amplifying 
power,  are  very  seldom  accurately  stated,  even  by  the  best 
makers.  If  it  is  necessary  to  know  the  exact  magnification  of 
any  object  with  any  objective  at  any  distance,  recourse  must 
be  had  to  measurement  by  a  stage  or  other  micrometer.  The 
lower  the  power  of  an  objective  the  more  difficult  it  is  to  give 
it  wide  angular  aperture,  consequently  objectives  which  pre¬ 
tend  to  wide  angles  are  usually  quoted  under  their  real  power, 
i.  e.,  over  their  real  focal  length.  And  tolerance  of  eye-piecing 
is  a  very  important  factor  in  calculations  as  to  power,  for  a 
quarter-inch  o.  g.  may  stand  an  ocular  of  twice  the  power  that  a 
one-sixth  can  bear,  and  so  after  all  the  one-fourth  may  come  to 
be  the  higher  power.  Well-made  objectives  will  give  good 
images  with  oculars  that  will  break  down  inferior  lenses,  and 
a  lens  before  purchase  should  always  be  tested  with  a  high 
ocular ;  there  is  no  better  trial  that  can  be  rapidly  made. 

There  are  certain  proverbial  tests  for  microscopic  objectives, 
and  a  glass  is  quoted  as  resolving  this,  that  or  the  other  test 
structure.  This  is  all  very  well  if  the  tester  be  the  owner  of 
the  test  object,  and  know  it  well.  But  opticians  always  have 
test  objects  of  their  own,  which,  we  need  not  say,  are  intended 
for  testing  lenses  to  the  satisfaction  of  would-be  purchasers. 
An  optician’s  podura  scale,  or  “blowfly’s  tongue,”  is  generally 


32 


PRACTICAL  PHOTO-MICROGRAPHY. 


easier  of  resolution  than  any  to  be  found  in  the  cabinet  at 
home,  and  an  optician  is  likely  to  choose  a  pretty  even  section 
of  an  echinus  spine  as  a  test  for  flatness  of  field.  Flatness  of 
field  is  a  highly  important  quality  in  an  objective  for  general 
photo-micrography,  and  depends  chiefly  on  skilful  work  on  the 
optician’s  part.  Want  of  this  quality  may  be  hidden  by  dia¬ 
phragms  in  the  ocular,  and  often  is  so  in  badly  made  apparatus. 

Finally,  it  may  be  said  that  the  tyro  microscopist  is  not 
capable  of  making  a  wise  selection  of  objectives  for  photo¬ 
micrography  or  any  purpose,  but  an  experienced  worker  will 
be  able  to  select  the  good  lenses  at  once  in  all  points  except 
actinic  correction,  and  on  that  point  the  optician’s  word  must 
be  taken  if  trial  of  the  lens  is  not  permitted.  The  beginner 
ought  therefore  to  get  a  skilled  friend  to  choose  the  lenses  for 
him.  We  should  consider  the  following  to  be  a  complete 
battery  of  objectives,  provided  they  were  of  first-class  con¬ 
struction  :  3  inch  ;  inch  or  2  inch ;  1  inch  ;  \ ;  | ;  -fa. 


CHAPTEK  TV. 


OPTICAL  APPARATUS  CONTINUED. 

The  Condenser  is  almost  of  equal  importance  with  the 
objective,  and  certainly  the  best  object  glass  cannot  be  expected 
to  work  at  its  best  without  a  good  condenser  properly  used. 
A  non-achromatized  object  glass  is  so  evidently  useless  that  no 
one  is  likely  to  be  taken  in  by  one,  but — perhaps  unfortunately 
— a  non-achromatic  condenser  is  often  found  a  very  tolerable 
makeshift  for  an  achromatic  one.  At  all  events,  those  who 
cannot  afford  to  buy  an  achromatic  condenser  need  not  despair 
of  producing  very  fine  work,  though  [perhaps  the  very  finest 
is  beyond  their  reach. 

For  the  lowest  powers  usually  employed  in  our  work,  how¬ 
ever  desirable  a  substage  condenser  may  be,  certain  diffi¬ 
culties  of  illumination  preclude  the  use  of  a  condenser,  and  a 
bull’s-eye  must  suffice.  But  for  all  objectives  of  one  inch  and 
higher  power  we  strongly  recommend  the  use  of  a  substage 
condenser  ;  the  bull’s-eye  also  may  be  used  if  necessary.  The 
cheaper  and  commoner  kinds  of  condenser  are  non-achromatic, 
consisting  usually  of  three  elements  and  varying  in  angular 
aperture  from  low  figures  up  to  the  numerical  aperture  1.4  as 
made  by  Zeiss  and  others,  the  latter  being  of  course  oil  immer¬ 
sion  condensers.  For  lower  power  work — up  to  (say)  the  ordi¬ 
nary  four-tenths  o.  g.  of  about  90  deg. — the  front  element  should 
be  removed  from  the  condenser ;  this  front  is  usually  fitted 
with  a  metal  cap  pierced  with  a  very  small  hole  for  centering 
purposes.  Even  the  third  or  lowest  element  may  be  used  alone 
as  a  condenser,  but  as  a  rule  it  is  better  either  to  use  the  two 
lower  elements  or  to  omit  the  condenser  entirely. 

Achromatic  Substage  Condensers  are  now  made  by  all 
opticians  and  used,  so  far  as  we  know,  by  all  good  micro- 
scopists  aiming  at  the  best  results  of  either  observation  or 


X 

34  PRACTICAL  PHOTOMICROGRAPHY. 

delineation.  These  condensers  are  usually  of  three  combina¬ 
tions,  and  range  to  the  highest  attainable  immersion  apertures. 
The  best  that  has  ever  come  under  the  notice  of  the  writer  is 
the  Apochromatic  Immersion  Condenser  of  Powell  and  Lea- 
land,  giving  an  immersion  angle  of  A.  A.  1.4  or  even  higher. 
The  focal  length  of  this  condenser  is  about  one-fifth  of  an  inch, 
so  that  in  the  absence  of  a  bull’s-eye — which  the  writer  never 
uses  with  this  condenser — the  illuminated  field  is  but  small 
unless  the  power  of  objective  used  be  high  ;  for  critical  work 
this  shortness  of  focus  is  an  advantage.  The  price  of  achro¬ 
matic  condensers  of  high  angle  is  considerable,  but  their 
superiority  over  non-achromatic  condensers  is  great.  Messrs. 
Beck,  Swift,  and  probably  all  opticians  make  achromatic 
condensers  to  nearly  the  full  extent  of  the  air  angle,  but  one 
of  140  deg.  will  be  found  a  very  useful  condenser  where  the 
pocket  does  not  permit  of  more  than  a  few  pounds  of  expense. 


Fig.  4* — Iris  Diaphragm. 


The  condenser,  as  will  be  more  fully  shown  hereafter,  is  not 
so  much  a  device  for  throwing  a  blaze  of  light  upon  the  object, 
as  for  (1st)  focusing  the  light  at  a  certain  point,  and  (2nd) 
modifying  the  angle  and  the  direction  of  the  light.  Accord¬ 
ingly  the  condenser  is  furnished  with  various  accessories  which 
must  be  named  here,  though  their  precise  use  must  wait  till  a 
later  time.  A  set  of  diaphragms  usually  accompanies  the  con¬ 
denser,  and  these  have  apertures  graduated  in  size  from  the 
full  aperture  of  the  optical  part  of  the  condenser  down  to  very 
small  holes,  the  smallest  of  all  usually  serves  for  centering.  An 
exceeding  great  convenience  is  the  Iris  Diaphragm,  Fig.  4, 


PRACTICAL  PHOTO-MICROGRAPHY. 


35 


the  nature  of  which  explains  itself  to  anyone  looking  at  onr 
cut.  The  manufacture,  however,  is  by  no  means  so  simple, 
and  the  purchaser  ought  to  see  that  the  interior  of  the  aperture 
is  as  nearly  circular  as  possible,  and  that,  in  closing,  the  seg¬ 
ments  do  not  “  jam,”  or  work  very  tightly,  a  very  common 
fault.  The  segments  should  not  “  lock,”  that  is  should  not 
interlace  with  each  other,  for  that  construction  generally 
means  a  “  jam.” 

Another  accessory  usually  accompanying  a  condenser  is  a 
set  of  “  black-ground  discs,”  the  nature  of  which  will  be  under¬ 
stood  from  figure  6  and  the  use  of  which  will  be  treated  later. 


Fig.  5. — Powell  and  Lealand’s  Apochromatic  Condenser  N.  A.  1. 4 

Frequently  also  other  “  stops  ”  accompanying  the  condenser, 
we  figure  three  of  them  here,  so  that  their  description  may  be 
recognised  when  we  come  to  mention  their  uses. 

#®®  © 

Fig.  6. — Stops. 

i 

There  are  various  other  accessories  frequently  fitted  to  the 
substage  of  a  microscope,  sometimes  to  be  used  along  witli  the 
condenser,  sometimes  independent  of  the  condenser.  Thus  a 
polariser,  with  or  without  selenite  discs,  is  often  made 
to  fit  the  substage;  colored  glasses,  technically  called  “light 
modifiers”  are  also  common  accompaniments  of  an  achro- 


36 


PRACTICAL  PHOTO-MICROGRAPHY. 


matic  substage  condenser.  Indeed,  condensers  are  frequently 
mounted  so  as  to  carry  all  or  several  of  the  accessories  described, 
and  to  carry  them  all  at  once ;  while  the  writer  admits  the 
ingenuity,  and  even  the  occasional  convenience  of  such 
arrangements,  he  hardly  ventures  to  recommend  their  use. 
Arrangements  of  this*  kind  are  apt  to  be  heavy,  clumsy,  bulky 
and  puzzling,  and  it  is  on  the  whole  better  to  have  on  the 
substage  at  the  time  of  work  only  as  many  of  these  accessories 
as  are  actually  in  use.  Still  it  may  suit  some  tastes  and  some 
purses  to  adopt  one  of  these  multiplex  arrangements,  and  one 
is  figured  here  as  a  sample  of  the  usual  article. 


Fig.  7. — A  Fitted  Substage  Condenser — Achromatic. — Swift. 

Another  common  contrivance  for  facilitation  of  work  and 
•  for  convenience  of  manipulation  is  a  nose-piece,  double,  triple, 
or  even  quadruple  (Fig.  8).  While  admitting  the  convenience 
of  this  contrivance  the  writer  does  not  recommend  its  use,  for 
delicate  work  at  all  events.  The  less  load  we  have  on  the 
microscope  tube,  especially  near  the  objective,  the  better; 
cases  have  occurred  of  injury  to  the  working  of  a  delicate  fine 
adjustment  screw  by  a  heavy  nose-piece.  Greatly  to  be 
preferred  for  efficiency  and  for  economy,  and  not  a  whit  behind 


PRACTICAL  PHOTO-MICROGRAPHY. 


37 


in  facility  and  elegance,  is  a  simple  adapter  with  a  bayonet 
joint  made  by  filing  away  part  of  the  thread  of  the  adapter, 
and  part  of  that  of  the  microscope  tube.  A  lens  can  be 
screwed  into  the  latter  in  the  usual  way  just  as  if  the  tube- 
thread  were  complete. 


Fig.  8. — Triple  Nose-piece. 


The  objective  screws  into  one  end  of  the  adapter  in  the  usual 
way,  then  the  other  end  of  the  adapter  is  pushed  straight  into 
the  threaded  end  of  the  microscope  tube  and  gets  a  short  turn 
in  one  direction,  when  it  is  at  once  clamped.  These  adapters 
are  easily  made,  small,  cheap,  and  several  can  be  had  for  a  few 
shillings. 

No  mention  has  been  yet  made  of  oculars,  because  the 
writer  has  no  confidence  in  any  ocular  except  those  made 
specially  for  projection,  and  projection  oculars  shall  be  treated 
in  a  separate  chapter  along  with  apochromatic  objectives.  It 
is  not  by  any  means  asserted  that  no  ocular  of  the  ordinary 
type  may  be  successfully  used  in  photo-micrography,  but  the 
writer  has  never  yet  been  satisfied  with  the  performance  in 
this  work  of  any  ocular,  achromatic  or  otherwise,  except  the 
projection  oculars.  It  is  not  denied  that  in  some  cases  good 
results  have  been  obtained  with  ordinary  eye-pieces,  but  the  . 
writer  has  never  yet  ascertained  on  what  fortuitous  circum¬ 
stances  the  success  has  depended.  “  Fortuitous  ”  is  written 
advisedly,  for  by  its  construction  an  ordinary  ocular  is  evi¬ 
dently  not  intended  to  project  an  image,  except  on  the  human 
retina.  It  is  to  be  noted  that  an  ordinary  objective  is  “  over¬ 
corrected,”  a  Huyghenian  ocular  under-corrected,  so  the  two 
often  balance  each  other. 


38 


PRACTICAL  PHOTO-MICROGRAPHY. 


Nor  does  the  writer  commit  himself  to  any  opinion  as  to  the 
merits  of  a  contrivance  known  as  an  “Amplifier,”  and  con¬ 
sisting  of  an  achromatic  concavo-convex  or  double-concave  lens 
inserted  behind  the  object  glass ;  he  has  not  himself  tried  such 
an  arrangement,  hut  has  seen  specimens  of  work  produced 
with  its  aid  which  do  not  seem  to  speak  highly  in  its  favor, 
though  jper  contra  he  has  seen  very  creditable  work  produced 
in  its  presence. 


Fig.  9. — Bulls’s-Eye  on  Stand. 


The  bull’s-eye  does  not  require  special  mention  in  this 
chapter ;  it  is  usually  a  plano-convex  glass  used  with  its  plane 
surface  next  to  the  radiant,  and  the  larger  it  is,  without  being 
clumsy,  the  better,  though  by  some  a  small  bull’s-eye  is  pre¬ 
ferred.  A  small  bull’s-eye,  having  a  shorter  focus,  gives  more 
brilliant  illumination  than  a  large  one. 


CHAPTER  Y. 


ILLUMINATION. 

Practically  we  have  to  consider  only  five  radiants :  Sun¬ 
light  direct,  daylight  diffused,  electric  light,  oxy-hydrogen 
limelight,  and  lamplight  from  some  form  of  oil  lamp.  Mag¬ 
nesium  light  we  must  at  once  put  aside,  because,  while  it  has 
been  successfully  used  for  exposures  of  very  brief  duration,  it 
is  out  of  the  question  for  prolonged  exposures  on  the 
scores  of  inconvenience  and  expense,  and  some  of  our 
objects  will  require  prolonged  exposures  to  any  light  how¬ 
ever  powerful.  The  light  produced  by  carburetted  hydro¬ 
gen  burned  at  the  orifice  of  an  ordinary  “  gas-burner  ”  has 
several  qualities  which  render  it  useless  for  our  purpose,  and 
no  system  known  to  us  of  burning  this  gas  alone  is  at  all  suited 
to  our  purpose.  Admittedly,  however,  the  incandescence  of 
certain  materials  impregnated  with  such  refractory  substances 
as  zirconium  salts,  the  incandescence  being  produced  by  ordin¬ 
ary  “gas  ”  suitably  used,  gives  some  promise  of  future  utility, 
though  as  yet  we  have  not  been  able  to  utilize  any  contri¬ 
vances  such  as  the  “  Welsbach  ”  burner,  and  efforts  on  our 
part  have  not  been  wanting. 

In  past  years,  before  our  photographic  preparations  had  at¬ 
tained  the  degree  of  sensitiveness  to  light  that  they  have  now, 
duration  of  exposure  was  often  a  very  important  considera¬ 
tion,  and  it  was  little  wonder  that  direct  sunlight  was  invari¬ 
ably  used  for  certain  work,  where  with  even  the  most  power¬ 
ful  of  artificial  lights  the  exposure  must  have  extended  to 
many  hours.  The  duration  of  exposure  is  per  se  of  little  con¬ 
sequence,  but  the  danger  of  tremor  and  change  of  tempera¬ 
ture  are  much  more  serious  matters. 

The  use  of  direct  sunlight  involves,  in  most  cases,  the  use 
of  a^heliostat,  and  in  all  cases  a  vast  amount  of  uncertainty. 


40 


PRACTICAL  PHOTO-MICROGRAPHY. 


In  Great  Britain,  at  all  events,  the  use  of  direct  sunlight  may 
be  set  aside  as  not  available,  certainly  as  not  presenting  suffici¬ 
ent  advantages  to  counteract  its  enormous  disadvantages,  and 
in  America  there  is  ho  longer  the  necessity  for  it  that  there 
was  in  the  days  of  Woodward’s  achievements.  No  work  on 
photo-micrography,  however,  could  pretend  to  be  complete 
without  something  more  than  an  allusion  to  sunlight  illumina¬ 
tion,  so  we  shall  present  a  diagram  of  the  arrangement  used  by 
Woodward,  an  arrangement  which  in  many  respects  formed 
the  basis  of  future  developments. 

Messrs.  Truan  and  Witt,  in  the  production  by  wet  collodion 
of  a  fine  series  of  photo-micrographs  representing  certain  Dia- 
tomaecae  of  Hayti,  used  an  apparatus  wherein  direct  sunlight 
was  projected  by  means  of  the  mirror  of  a  Chevalier  megascope. 

Dr.  Woodward,  after  using  the  arrangement  figured 
No.  10,  made  alterations  which  he  considered  improvements 
and  which  in  some  respects  undoubtedly  were  steps  in  the 
right  direction.  He  used  a  room  as  his  camera,  supporting  his 
sensitive  plate  on  an  easel  which  was  made  to  run  on  rails  to 
and  from  the  microscope  which,  with  objectives,  was  fixed  to 
the  window  shutter,  the  light,  as  before,  being  reflected 
through  the  optical  system  by  a  heliostat,  The  obvious  disad¬ 
vantage  of  this  arrangement  was  the  fact  that  in  case  of  any 
tremor  the  sensitive  plate  and  the  optical  system  might  not 
move  together.  Dr.  Maddox  used  also  a  darkened  room,  but 
he  had  in  the  room  a  camera,  reflecting  the  sunlight  by  means 
of  a  mirror  and  prism  through  the  optical  system  which  was 
fitted  to  a  hole  made  in  the  shutter.  Non-actinic  light  was  ad¬ 
mitted  into  the  room  by  means  of  suitable  “  light-filtering  ” 
media.  Many  other  arrangements  might  be  mentioned  with¬ 
out  any  notable  difference  from  or  superiority  over  these 
already  touched. 

An  important  feature  in  sunlight  illumination  is  the  use 
of  “monochromatic”  light.  The  reader  is  probably  aware 
that  the  rays  composing  a  beam  of  white  light  are  not  all 
equally  energetic  in  producing  the  chemical  action  necessary 
to  the  production  of  a  photographic  image.  The  waves  of 
light  producing  the  sensation  of  sight  vaiy  in  length  from 


PRACTICAL  PHOTO-MICROGRAPHY. 


41 


Fig.  10.  (From  Dr.  Beale’s  **  How  to  Work  with  the  Microscope. 


42 


PRACTICAL  PHOTOMICROGRAPHY. 


crest  to  crest,  from — roughly — -jtoto  th  to  s  g  „  0  6  tli  of  an  inch ; 
and  of  these  varying  wave-lengths  those  which  exercise  the 
greatest  chemical  action  measure  about  e-4  l  0  Qth  of  an  inch, 
and  are  what  we  call  “violet”  in  color.  If,  then,  we  can  cut 
off  all  rays  except  those  which  exercise  strong  chemical  action, 
we  shall  reduce  the  general  actinic  force  of  the  white  ray, — for 
all  visible  rays  have  some  actinism, — but  we  shall  have  less 
confusion  among  the  rays  producing  the  photographic  image, 
and  so  our  optical  apparatus  will  probably  be  used  at  its  best, 
especially  if  our  lenses  are  corrected  for  the  rays  which  pro¬ 
duce  the  best  visual  effect,  as  lenses  naturally  are  when  in¬ 
tended  for  ocular  observation  only.  Two  methods  were  in 
vogue  for  this  passing  of  actinic  rays  alone :  one  was  the  use 
of  a  cell  containing  cupric  ammonio-sulphate  dissolved  in 
water,  which  makes  a  blue  solution,  and  one  spectroscopically 
suitable  for  the  purpose  aimed  at ;  *  the  other  plan  consisted 
in  the  use  of  a  prism  which  broke  up  the  white  ray  into  its 
component  parts,  the  blue  part  alone  being  allowed  to  pass 
through  the  microscope.  A  “  diffraction  grating  ”  would  yield 
a  still  purer  spectrum,  but  so  far  as  we  know  has  not  been  used 
for  this  purpose.  In  each  case  the  solar  ray  was  passed  through 
the  monochromatising  medium  before  it  reached  the  object. 

Diffused  daylight  may  be  utilized  by  reflection  from  white 
cloud  or  uniform  blue  sky;  but  after  repeated  and  careful 
experiments  the  writer  can  not  recommend  this  system  of 
illumination  as  likely  to  prove  satisfactory  to  the  serious  photo- 
micrographer.  If  white  cloud  or  homogeneous  sky  can  be 
depended  on,  the  ordinary  plane  mirror  of  the  microscope,  if 
of  ample  size,  will  answer ;  all  rays  in  this  case  being  practi¬ 
cally  parallel  at  their  impact  on  the  mirror.  Another  plan, 
tested  by  the  writer  with  greater  success,  is  to  omit  the  mirror 
and  to  replace  it  by  a  white  surface,  as  very  fine  filter  or  blot¬ 
ting  paper,  but  not  a  shiny  surface  as  sized  paper  or  opal  glass 
The  white  surface  is  to  be  inclined  in  a  suitable  direction  at  an 
angle  of  about  45  deg.  to  the  axis  of  the  optical  system. 

*This  solution  is,  in  the  writer’s  experience,  usually  far  from  monochro¬ 
matic  and  decidedly  inferior  to  certain  qualities  of  cobalt  blue  glass  for 
this  purpose. 


PRACTICAL  PHOTO-MICROGRAPHY. 


43 


The  electric  light  has  been  used  with  great  success  in  this 
connection,  an  arc  lamp  having  been  the  usual  form.  There 
is  no  doubt  that  an  arc  light,  provided  it  is  steady,  may  be 
expected  to  work  grandly  for  our  purpose.  It  is  in  most  cases, 
however,  expensive,  difficult  to  work  to  perfection,  and  when 
imperfectly  worked,  a  very  serious  botheration.  As  the  writer 
has  no  experience  of  the  arc  light  he  refrains  from  making 
any  statements  as  to  its  suitability  or  unsuitability  for  our  pur¬ 
pose.  Incandescent  filaments  in  electric  lamps  might  be  made 
answerable  to  our  purpose,  but  so  far  as  we  know  no  incan¬ 
descent  electric  lamp  has  yet  been  found  equal  even  to  a  good 
oil  lamp,  the  area  of  incandescence  being  too  slender  in  the 
former. 


Fig.  11. — Oxy-Hydrogen  Tet  by  Newton.  Author’s  “  Cut-off.” 


The  writer  uses  the  lime  light  as  his  radiant  in  nearly  all  his 
work,  and,  taken  as  a  whole,  this  light  is  as  nearly  perfect  for 
the  purpose  as  any  illuminant  at  present  known.  The  general 
form  of  a  lime-jet  is  well  known,  and  the  ordinary  form  of 
“blow-through”  or  “mixing”  jet  will  doubtless  suffice  for  all 
purposes.  The  blow-through  jet  gives  a  larger  area  of  incan¬ 
descent  lime,  but  the  incandescence  is  not  so  perfect,  nor  the 
color  nearly  so  good  as  that  produced  by  the  mixed  gases. 
There  is  no  necessity  for  any  great  pressure  of  the  gases,  pro¬ 
vided  the  proportion  of  one  gas  to  the  other  is  suitable,  and 
the  nipple  of  the  jet  has  a  bore  suitable  to  the  other  circum¬ 
stances.  All  these  matters  maj  be  settled  by  experiment,  and, 
in  fact,  must  be  so  settled.  The  writer  uses  a  mixing  jet,  but 
takes  the  hydrogen  direct  from  the  house  main,  while  he  puts 
the  oxygen  in  a  bag  and  puts  thereon  only  a  moderate  pressure ; 


44 


PRACTICAL  PHOTOMICROGRAPHY. 


in  fact,  on  a  pressure  board  four  feet  by  three  feet,  he  places  a 
weight  of  forty  pounds.*  Figure  11,  representing  a  jet  arrange¬ 
ment  designed  by  the  writer,  requires  some  explanation. 

The  jet  is  an  ordinary  mixing  jet,  but  has  an  extra  attach¬ 
ment  consisting  of  three  cogged  wheels  worked  from  the  back 
of  the  jet  by  the  cross  piece  and  operating  two  taps,  one  on 
the  O  and  the  other  on  the  H  tube.  These  tubes  are  operated 
proportionally  by  the  equal  cogged  wheels,  so  that  the  light 
being  once  arranged  at  its  best,  both  of  these  extra  taps  being 
full  open,  the  brilliance  of  the  light  can  be  lessened  without 
injury  to  the  quality  by  simply  turning  the  cross-piece.  But 
the  H  tap  has  a  “bye  pass,”  so  that  the  hydrogen  can  not  be 
entirely  cut  off  by  this  tap,  while  the  oxygen  is  a  complete  cut 
off.  The  result  is  that  the  lime  never  gets  quite  cold  when 
the  gases  are  not  turned  up,  and  there  is  no  need  to  light  the 
jet  each  time  after  it  has  been  temporarily  out  of  use.  More- 
over,  by  lowering  the  gases  together  the  worker  saves  his  eyes, 
and  by  turning  the  extra  arrangement  entirely  down  leaving 
only  a  glimmer  of  hydrogen  burning,  the  worker  saves  his 
time,  his  lime  and  his  money.  The  harder  the  lime  the  bet¬ 
ter  for  our  purpose,  for  a  large  area  of  incandescence,  unequal 
in  brilliance  and  color,  is  most  puzzling  and  pernicious.  The 
jet  figured  is  made  by  Messrs.  Newton  &  Co.,  of  London, 
but  is  open  to  the  public,  being  in  no  way  “protected.”  For 
a  very  brilliant  light  with  a  small  incandescent  area — as  for 
work  of  the  greatest  delicacy — both  gases  should  be  put  under 
heavy  pressure  in  bags,  or  preferably,  cylinders.  Mr.  E.  M. 
Nelson  has  his  gases  in  iron  tanks,  and  gets  a  very  fine  light 
indeed. 

The  writer  has  on  several  occasions  attempted  to  work  out 
some  medium  to  replace  “  limes  ”  which  crack  at  awkward 
times,  and  are  at  all  times  liable  to  disintegration  through  ac¬ 
cess  of  damp.  Magnesia  pounded  very  thoroughly  for  two 
hours  in  a  mortar  with  sufficient  water  to  form  a  paste  prom¬ 
ised  well.  “  Buttons  ”  were  made  with  the  paste,  each  button 

*  Since  the  introduction  of  Beard’s  excellent  “  Regulator,”  the  writer 
has  given  up  bags,  and  uses  oxygen  from  the  cylinder,  pressure  being 
controlled  by  the  regulator. 


PRACTICAL  PHOTO-MICROGRAPHY. 


45 


impaled  with  a  short  length  of  platinum  wire,  and  then  gradu¬ 
ally  dried,  first  in  a  heated  iron  oven,  then  in  coal  gas  flame, 
lastly  in  the  oxy-hydrogen  flame,  as  suggested  by  Dr.  Roux  of 
Paris;  but  the  result  seemed  decidedly  inferior  to  the  ordin¬ 
ary  lime.  Zirconium  oxide  was  also  tried  with  no  better 
success. 


Fig.  12. — Swift’  Microscope  Lamp. 

Probably  most  of  our  readers  will  find  an  oil  lamp  answer 
all  desired  purposes,  and  if  time  be  no  object,  a  good  oil  lamp 
will  probably  prove  entirely  satisfactory.  If  the  wick  be 
single  and  flat,  and  if  it  can  be  turned  either  broadside  or  edge 
to  the  microscope,  the  kind  of  lamp  is  practically  immaterial. 
But  lamps  are  made  specially  for  this  work  and  several  of 
them  may  safely  be  recommended.  Mr.  Swift’s  lamp  (fig.  12), 
for  instance,  has  served  the  writer  thoroughly  well,  and  the 
lamp  figured  No.  13  is  also  well  adapted  for  this  work. 


46 


PRACTICAL  PHOTO-MICROGRAPHY. 


The  lamp  should  be  on  a  heavy  stand,  and  for  convenience 
should  slide  up  and  down  a  stem  as  shown  in  our  cuts.  About 
an  ounce  of  camphor  may  be  added  to  each  pint  of  the  oil  used, 
which  should  be  paraffin  of  the  very  finest  quality  that  can  be 
obtained.  Bad  oil  causes  no  end  of  trouble.  The  wick  must 


Fig.  13. — Baker’s  “Nelson”  Lamp. 


be  kept  well  trimmed,  and  all  parts  of  the  lamp  scrupulously 
clean.  The  slips  of  glass  used  in  front  of  the  flame  in  the 
metal  chimney  are  very  apt  to  break  when  the  flame  is  turned 
edge  toward  the  microscope ;  to  prevent  this  the  slips  should 
be  rolled  in  a  piece  of  cloth  and  boiled  for  two  hours  in  water, 
or,  still  better,  in  sweet  oil. 


*  \ 


No.  1. — Hairs  on  Proboscis  of  Blowfly,  X  375. 


No.  Z. — Injected  Villi,  Intestine  of  Rabbit,  X  30. 


Plate  I. 


CHAPTER  Y I. 


PHOTO-MICROGRAPHIC  APPARATUS. 

After  what  has  been  written  about  the  component  parts, 
the  entire  system  of  apparatus  ought  to  be  easily  understood. 
Ho  matter  what  microscope-stand  or  what  light  is  to  be  used, 
some  ingenuity  and  care  will  be  required  to  fit  the  several 
parts  together  so  that  the  action  of  the  whole  may  be  efficient 
and  sure.  If  a  complete  photo-micrographic  apparatus  be 
bought  ready  for  use,  of  course  the  purchaser,  having  once 
satisfied  himself  of  the  accuracy  and  convenience  of  the 
apparatus,  need  no  further  trouble  himself  on  this  score. 

Exceedingly  good  work  has  been  done  and  may  be  done 
again  without  any  special  apparatus  beyond  a  microscope  and 
a  camera.  The  microscope  has  only  to  be  turned  to  the 
horizontal,  a  camera  run  up  to  the  eye  piece  end  of  the  micro¬ 
scope,  all  light  not  passing  through  the  optical  system  excluded 
by  means  of  a  velvet  tube  or  cone  passed  from  a  photographic 
lens  tube,  (the  glasses  being  removed)  to  and  over  the  end  of 
the  microscope  tube,  the  whole  presenting  an  appearance 
somewhat  as  shown  in  fig.  14. 


Fig.  14. — Simple  Arrangement  of  Microscope  and  Camera. 


It  need  hardly  be  said  that  with  such  an  arrangement  great 
care  is  necessary  to  prevent  shaking,  and  to  preserve  the  due 
relation  of  parts.  In  all  apparatus  for  this  purpose  two  salient 


48 


PRACTICAL  PHOTOMICROGRAPHY. 


necessities  must  be  attended  to  ;  1st.  The  light,  the  condensing 
system,  the  object  glass  and  the  centre  of  the  sensitive  plate 
must  all  be  axially  centred  to  each  other ;  and  2nd.  The  object 
and  the  sensitive  plate  must  be  parallel  to  each  other  and  per¬ 
fectly  perpendicular  to  the  optical  axis  of  the  system.  The 
slightest  divergence  from  either  of  these  relations  will  entail 
failure.  / 

Where  the  intending  photo-micrographer  possesses  the  com¬ 
ponent  parts  of  the  system,  as  microscope,  lamp,  and  camera, 
and  requires  only  to  fix  these  in  suitable  position  on  some  base 
to  be  used  permanently,  the  matter  lies  chiefly  with  himself, 
and  the  ease  of  his  operations  will  depend  chiefly  on  the  instru¬ 
ments  he  happens  to  have.  We  shall  figure  and  describe  two 
arrangements  at  least;  one  a  sample  of  an  apparatus  sold  ready 
made,  the  other  an  apparatus  built  up  of  miscellaneous 
materials  by  the  writer,  and  these  are  given  merely  as  sug¬ 
gestions  and  as  examples  of  what  has  been  found  to  work  well 
in  the  writer’s  hands. 

In  Britain  of  late  years,  several  opticians  have  stocked 
apparatus  of  which  figure  15  is  a  type.  It  presents  all  the 
useful  features  of  its  class,  though  other  instruments  are  to  be 
found  differing  in  detail,  some  details  being  superior,  others  in¬ 
ferior,  to  those  seen  in  the  cut. 

This  apparatus  was,  the  writer  believes,  designed  in  the  form 
shown  by  Professor  E.  M.  Crookshank,  and  used  by  him  in 
his  photo- micrography  of  Bacteria.  The  writer  has  used  an 
apparatus  in  all  essential  points  similar  to  that  figured,  and 
had  great  satisfaction  in  its  use.  The  stand  is  so  made  that 
when  it  is  necessary  to  have  the  stage  of  the  microscope 
horizontal,  as  shown  in  Fig.  15,  as  when  for  photography  of 
liquid  matter,  the  base  board  can  be  let  down  to  the  vertical 
position ;  as  every  part  of  the  optical  and  photographic  and 
illuminating  systems  is  clamped  to  the  base  board,  this  position 
is  easily  attained  ;  and,  except  where  a  lamp  burning  same 
liquid  is  used,  one  position  is  as  manageable  as  the  other.  If 
an  oil  lamp  furnishes  the  light  a  mirror  must  come  into  requis- 
tion.  A  point  on  which  the  writer  lays  great  stress  is :  the 
microscope,  condensing  system  and  radiant  are  all  fixed  to  one 


49 


PRACTICAL  PHOTO-MICROGRAPHY. 

£ 

platform  which  turns  or  a  central  pivot,  so  that  the  optical 
system  can  he  turned  out  from  the  axial  line  of  the  entire  sys- 


Fig.  15. — Photo-Micrographic  Apparatus  by  Swift,  shown  at  the 

Vertical  Position. 

tern,  the  object  can  be  examined,  corrections  of  the  objectives 
studied,  and  everything  focused  and  centered  with  the  eye- 


50  PRACTICAL  PHOTOMICROGRAPHY. 

* 

piece,  the  operator  being  in  a  comfortable  and  convenient 
position,  sitting  or  standing,  as  desired.  These  things  being 
done,  the  platform  is  turned  back  to  a  “stop”  which  is  so 
arranged  by  the  maker  of  the  apparatus  that  the  optical  sys¬ 
tem  is  then  axially  centered  with  the  photographic  system. 
The  focusing  on  the  plane  of  the  sensitive  plate  alone  remains 
to  be  performed,  and  this  is  done  by  means  of  the  rod  seen  in 
the  cut.  The  rod  has  a  pulley,  tiie  fine  adjustment  has  a  screw 
with  a  grooved  milled  head,  and  a  pulley  passing  over  the  rod- 
pulley  and  round  the  grooved  milled  head  operates  the  fine  ad¬ 
justment  at  the  will  of  the  operator  examining  the  image  on 
the  focusing  screen  of  the  camera.  A  “  Hooke’s  Joint  ”  may 
be  used  in  place  of  this  focusing  arrangement,  the  writer  used 
that  contrivance  for  some  time,  but  on  the  whole  an  arrange¬ 
ment  with  rigid  rod  and  pulleys  is  to  be  preferred. 

Figure  16  shows  the  writer’s  latest  arrangement,  which 
combines  some  ideas  gathered  from  Mr.  Kelson’s  apparatus 
with  others  of  the  apparatus  last  figured,  and  still  others  which 
occurred  one  by  one  to  the  writer  as  he  advanced  in  experi¬ 
ence.  The  platform  carrying  light  and  optical  system  and 
turning  on  its  pivot  is  retained,  so  also  is  the  rigid  rod  and 
pulley  contrivance.  The  platform  is  still  “  stopped  ”  at  a 
certain  point,  but  this  time  the  camera  is  entirely  free  on 
a  very  heavy  teak  base  to  which  al*o  the  swinging  platform 
is  attached.  In  Fig.  15,  after  the  optical  part  is  stopped  at 
the  axis,  the  front  only  of  the  camera  is  run  forward  to  meet 
the  ocular  end  of  the  microscope  tube ;  but  in  Fig.  16  the  whole 
camera  is  pushed  forward  to  the  cap  on  the  tube,  and  in  both 
cases  a  smaller  cap  fixed  to  the  camera  fits  very  loosely  inside 
a  larger  cap  on  the  microscope  tube.  There  is  no  difficulty  in 
centering  the  latter  arrangement,  Fig.  16,  for  the  centre  of 
the  camera  focusing-screen  is  marked,  and  if  the  centre  of 
the  object  coincides  with  the  centre  of  the  ground  glass 
everything  must  be  centered  and  perpendicular  to  the  general  • 
axis. 

Any  photographic  camera  will  answer  for  this  work  pro¬ 
vided  it  be  light-tight,  and  reasonably  well  made.  No  “  mo¬ 
tions,”  such  as  “  swing-backs,”  are  required.  The  camera 


PRACTICAL  PHOTO-MICROGRAPHY 


51 


shown  in  Fig.  16  is  one  for  a  plate  7^x5^  inches  that  hap¬ 
pened  to  be  in  the  writer’s  possession.  The  bellows  arrange¬ 


ment  is  very  useful  though  not  essential,  and  the  same  applies 
to  the  rack  and  pinion.  The  available  stretch  of  the  camera, 


52 


PlijCTICAL  PHOTOMICROGRAPHY. 


including  the  supplementary  tapered  bellows  seen  in  front,  is 
30  inches  without  using  the  rack  and  pinion  ;  an  extra  length 
of  10  inches  can  be  added  at  will.  The  writer  has  an  attach¬ 
ment  to  the  apparatus,  Fig.  16,  by  which  he  can  increase, 
his  stretch  of  camera  to  7  feet  6  inches,  and  his  plate  to  10x8 
inches,  but  this  is  hardly  ever  used  and  never  has  been  used 
with  real  success.  A  stretch  of  40  inches  from  micro- tube  to 
plate  is  perhaps  the  limit  of  utility,  for  very  few  object  glasses 
will  stand  more  than  that  stretch  in  the  writer’s  experience, 
especially  with  oculars. 

The  largest  useful  size  of  plate  is  about  7x5  inches,  or  what 
is  called  in  England  “half-plate,”  6-|x4£  inches.  The  camera 
should  take  a  plate  of  one  of  these  sizes,  but  should  have  “  car¬ 
riers  ”  or  “  kits  ”  fitting  the  “  dark  slide  ”  to  take  5x4  or 
4|x3£  plates,  the  latter  being  technically  called  “quarter- 
plates.”  Square  plates  are  probably  better  than  oblong  ones 
as  a  rule,  so  that  the  carriers  may  be  made  for  4^  inch  square 
plates,  but  plates  of  unusual  sizes  are  not  so  readily  obtained 
as  common  sizes.  * 

One  point  regarding  the  dark  slide  is  very  important ;  it 
should  on  no  account  slide  into  its  position  in  the  camera  by  a 
long  groove,  but  should  be  so  made  as  to  slide  only  about  an 
inch,  or  better  still  it  should  fall  into  a  groove  at  the  lower  side 
and  be  held  into  position  by  a  catch  at  the  top.  There  is  very 
little  danger  of  light  fog  in  this  region  of  our  apparatus, 
especially  as  the  room  should  be  darkened  (see  later); 
and  there  is  very  great  danger  of  moving  some  part  of  the 
apparatus  after  all  is  focused  if  the  operator  has  to  exert  any 
force  to  shove  the  slide  into  position.  The  shutter  of  the  dark 
slide  must  also  work  very  easily  and  sweetly  for  the  same 
reason. 

The  camera  has  of  course  a  “  ground  glass,”  which  is  used 
for  preliminary  examination  of  the  image  upon  the  screen,  and 
in  certain  cases  the  ground  glass  if  finely  ground  is  all-sufficient. 
In  any  case  the  ground  surface  may  with  advantage  be  oiled  ; 
but  even  then  the  surface  is  too  coarse  for  focusing  images 
with  very  fine  details.  Many  devices  have  been  used  and 
recommended  for  producing  a  surface  sufficiently  fine  yet  with 


PRACTICAL  PHOTOMICROGRAPHY. 


53 


sufficient  grain  to  show  an  image.  A  sensitive  gelatine  plate 
exposed  for  a  second  to  light,  developed,  fixed,  washed  and 
slightly  treated  with  mercuric  bichloride  gives  a  good  surface; 
this,  we  believe,  orginated  with  Mr.  "Walmsley.  No  better 
focusing  surface  will  be  found  than  a  piece  of  glass  with  some 
diamond  marks  on  the  front — that  is  on  the  side  next  the 
light.  In  the  writer’s  case  these  marks  consist  of  a  cross,  the 
arms  of  which  are  inches  divided  into  tenths  with  a  diamond ; 
when  viewing  the  image  with  the  focusing  eye-piece,  if  the 
magnification  be  known,  it  is  easy  to  measure  objects  and  dis¬ 
tances  at  a  glance.  No  image  can  be  seen  on  the  plain  glass 
unless  an  eye-piece  be  used  to  focus  the  aerial  image ;  the  glass 
in  fact  is  used  only  as  a  rest  for  the  focusing  eye-piece.  The 
eye-piece  used  is  known  as  a  Ramsden,  or  perhaps  better  a 
Zeiss  “  aplanatic  magnifier  ”  may  be  used.  In  either  case  the 
scratches  on  the  front  of  the  focusing  glass  must  be  most  care¬ 
fully  focused  with  the  eye-piece  ;  if  is  found  difficult  to  focus 
the  scratches,  a  fly’s  wing  or  some  such  object  may  be  fixed  to 
the  front  of  the  glass*  plate  and  the  magnifier  set  to  focus  on 
that.  It  goes  without  saying  that  the  focusing  screen — or 
ruled  glass  or  whatever  it  is — should  be  in  the  same  plane  as 
that  occupied  later  by  the  sensitive  plate.  The  rays,  however, 
in  ordinary  work  are  at  the  sensitive  plate  so  nearly  parallel 
that  slight  “  want  of  register  ”  between  plate  and  focus-screen 
is  not  so  very  fatal  as  many  think.  Dr.  Bousfield,  whom  no 
one  need  fear  to  follow,  uses  no  glass  plate  at  all,  nor  fixes  his 
focusing  eye-piece  at  any  point  as  many  do,  but  focuses  the 
aerial  image  in  air  alone ;  none  the  less  the  glass  plate  affords 
a  convenient  rest  for  the  Ramsden  or  Aplanatic,  but  there 
must  be  no  heavy  pressure  of  focuser  on  screen. 

There  are  many  other  ways  of  producing  a  focusing  screen 
but  probably  the  best  have  been  here  noticed. 

It  is  important  to  have  an  arrangement  inside  the  camera  for 
starting  and  stopping  the  exposure.  At  “  7  ”  on  Fig.  16 
is  seen  the  exterior  of  a  simple  flap  shutter,  the  flap  inside  be¬ 
ing  operated  by  the  button  outside.  Sometimes  when  a  very 
rapid  exposure  is  required  and  when  consequently  there  is  fear 
of  moving  the  whole  apparatus,  we  close  this  flap,  open  the  dark 


54 


PRACTICAL  PHOTO-MIUB^APHY. 


slide  shutter  in  the  usual  way,  then  taking  a  square  of  blackened 
cardboard  in  (say)  the  right  hand  and  holding  it  close  behind, 
but  not  touching  the  substage  condenser  so  as  to  shut  all  light 
from  the  object,  we  open  the  flap  with  the  left  hand  and 
swiftly  raise  and  lower  the  card  in  the  right  hand,  thereafter 
immediately  closing  the  flap.  Where  the  hand  is  unable  to  make 
a  sufficiently  quick  exposure,  we  rig  up  a  photographic  instan¬ 
taneous  shutter  between  light  and  condenser,  and  proceed  with 
this  shutter  on  the  same  principles  as  we  did  with  the  card¬ 
board. 

There  is  a  fine  field  open  to  the  mechanic  in  the  designing  of 
apparatus  for  photo-micrography ;  but  the  writer  can  only  say 
that  after  long  and  varied  work  with  the  apparatus,  figured 
No.  16,  which  was  put  together  chiefly  by  Mr.  Baker  of 
London,  he  is  at  a  loss  to  suggest  any  improvement  on  it. 

A  cell  or  trough  of  wood  with  plate-glass  sides  contains  a 
saturated  solution  of  common  alum  or  in  certain  cases  a  solu¬ 
tion  of  cupric  ammonio-sulphate.  These  solutions,  or  the  water 
of  them,  should  be  well  boiled  to  drive  off  air,  which,  if  the 
boiling  is  omitted,  rises  in  bubbles  from  the  bottom  when  the 
solution  begins  to  get  heated  as  it  does  with  the  oxyhydrogen 
limelight.  This  alum  cell  is  necessary  when  the  limelight  or 
any  other  illuminating  arrangement  generating  considerable 
heat  is  used.  In  high-power  work  changes  of  temperature 
have  a  very  marked  effect  on  the  sharpness  of  image  in  the 
negative.  (See  Fig.  16,  2.) 


CHAPTER  VII. 


REQUISITES  FOR  PHOTOGRAPHY. 

Haying  already  remarked  upon  the  advantages  of  ample  dark¬ 
room  accommodation,  running  water  and  a  waste-sink,  we  may 
now  enter  somewhat  into  detail  regarding  dark-room  arrange¬ 
ments  and  articles  used  in  operations  purely  photographic. 

In  arranging  for  non-actinic  illumination  the  reader  is  ad¬ 
vised  to  prepare  himself  at  the  outset  for  u  color  correct  ”  or 
“  orthochroinatic  ”  photography,  for  the  worker  at  general 
photo-micrography,  if  he  pay  any  attention  whatever  to  the 
words  of  the  author  of  this  book,  will  very  early  find  himself 
using  color-sensitive  plates.  This  means  that  whether  the 
the  reader  proposes  to  use  as  a  general  rule  yellow  diffused,  or 
clear  ruby  light,  he  must  provide  himself  at  all  events  with 
ruby  illumination.  If  development  is  to  be  conducted  by  day¬ 
light  we  recommend  that  the  outer  sash  of  the  window  be 
glazed  with  yellow  glass,  or  at  least  three  thicknesses  of  “  can¬ 
ary  medium”  known  to  all  photographic  dealers.  For  ordin¬ 
ary  plates  a  sash  of  ruby  glass  should  be  added  to  the  yellow 
glass,  and  the  best — in  fact  practically  the  only  good  ruby 
glass — is  “  flashed  ruby  ”  on  one  side  and  “  stained  yellow  ”  on 
the  other.  A  splendid  glass,  if  it  can  be  got,  is  flashed  deep 
ruby  on  one  side  and  ground  on  the  other  side.  The  three 
thicknesses  of  canary  medium  may  suffice  if  the  light  shining 
on  it  be  not  very  strong,  and  if  a  thickness  of  good  ruby  glass 
be  added,  or  two  layers  of  good  “  ruby  fabric,”  the  window  is 
probably  trustworthy  for  even  ortho-chromatic  plates.  If  arti¬ 
ficial  light  be  used  the  flashed  and  stained  ruby  glass  may  suf¬ 
fice  in  a  single  thickness  for  even  color-correct  plates,  though 
this  must  be  tested  ;  it  will  almost  certainly  suffice  for  any  or¬ 
dinary  plates;  two  thicknesses  of  the  canary  medium  for 
ordinary  plates,  with  the  addition  of  ruby  glass  as  before  for 


56 


PRACTICAL  PHOTO-MICROGRAPHY. 


“  ortho  ”  plates,  may  be  taken  as  “  safe.”  To  test  a  light  for 
safety,  place  a  plate  of  the  kind  to  be  used  half  in  the  leaves  of 
a  book,  expose  for  (say)  four  minutes  at  the  spot  where  the 
operation  of  development  is  to  be  conducted,  thereafter  de¬ 
velop  the  plate  as  much  as  possible  in  total  darkness,  and  it 
will  be  easy  to  discover  if  the  light  is  unsafe,  for,  if  it  is  un¬ 
safe,  the  half  that  projected  from  the  book  will  “  take  a  tint,”  in 
other  words,  will  develop  darker’  than  the  part  which  the  book 
protected.  It  is  vastly  important  in  photo-micrography  to  see 
exactly  what  the  plate  does  under  development,  but  in  order  to 
examine  the  plate  critically,  no  great  space  of  time  is  necessary; 
the  rationale  of  the  light  question  may  therefore  be  summed 
up :  Use  the  greatest  possible  amount  of  safe  light,  but  do 
not  waste  any  light ;  that  is,  do  not  expose  the  plate  to  light, 
however  safe,  when  no  object  is  gained  by  such  exposure. 

Uon-actinic  lamps  are  held  in  stock  by  all  photo  dealers;  we 
figure  one : 


Fig.  17.— Dark  Room  Lamp.— Carbutt. 


A  wooden  sink  lined  with  sheet  lead  seems  preferable  to  iron 
or  earthenware,  and  in  the  sink  should  be  a  wooden  “  hatch  ” 
or  grating  on  which  measures,  bottles,  etc.,  may  stand  and 
drip.  On  one  side  at  least  of  the  sink  should  be  a  ledge  or 
table  sloping  down  to  the  sink  and  lined  with  lead  or  covered 
with  rubber  or  American  cloth,  so  that  dripping  dishes,  etc., 
may  be  laid  on  the  slope  and  their  drippings  run  into  the  sink. 


PRACTICAL  PHOTOMICROGRAPHY. 


57 


The  end  of  the  water-tap  should  have  a  thread  by  which  may 
be  coupled  on  to  it  such  conveniences  as  a  rose,  a  rubber  tube, 
etc.  If  none  of  these  conveniences  can  be  had,  the  worker 
must  content  himself  with  a  jug  of  water,  or  a  vessel  with  a 
rubber  tube  provided  with  a  tap  or  a  spring  clip,  the  vessel 
being  placed  at  some  height,  as  on  a  chair  standing  on  the 
table.  Convenient  collapsible  rubber  sinks  with  waste  pipe 
can  be  had  in  Britain  and  probably  in  America.  In  photo¬ 
micrography  as  in  all  things  we  must  “  Cut  our  coat  according 
to  our  cloth.” 

A  set  of  flat  “  developing  dishes  ”  are  necessary  and  not  ex¬ 
pensive.  Two  of  these,  the  proper  size  for  the  plate  to  be 
used  may  be  made  of  papier-mache  or  ebonite ;  they  should  be 
black.  Two  others,  large  enough  to  hold  three  or  four  of  the 
plates  may  be  of  porcelain  and  should  be  white. 


Fig.  18. — Developing  Tray. 

Other  dishes  may  be  required  for  printing  and  other  pur¬ 
poses  ;  their  uses  will  be  seen  as  we  proceed. 

Some  filter  funnels ;  glass  measures,  say  10-oz.,  2-oz.  and  2 
drams ;  scales  and  weights;  a  drying  rack,  Fig.  19  ;  and,  as  a 
luxury,  a  washing  trough,  Fig.  20,  may  complete  this  branch 
of  the  outfit,  which  a  few  dollars  will  cover.  For  those  who 
object  to  slightly  stained  fingers,  a  hook,  Fig.  21,  and  a  “  pneu¬ 
matic  holder,”  Fig.  22,  may  be  added. 


58 


PRACTICAL  PHOTO-MICROGRAPHY. 


The  following  apparatus  will  be  required  beyond  the  things 
already  mentioned : 


Fig.  19. — Dry-Rack. 


Fig.  20. — Wash-Trough. 


For  all  kinds  of  contact  printing:  Printing  frames  (see 
later). 

For  enlarging  and  reducing — which  may  be  postponed  till 
some  practice  has  been  gained  in  other  works :  A  suitable  cam¬ 
era,  or  arrangement  of  other  cameras  (see  later) ;  also  a  suitable 
photographic  lens. 


Fig.  22. — Pneumatic  Holder. 


A  squeegee.  Some  glass  plates  or  ebonite  sheets  a  good 
deal  larger  than  the  largest  negatives  to  be  made  direct. 


PEAOTIOAL  PHOTOMICROGRAPHY. 


59 


The  following  articles  are  useful :  A  “  W arnerke  sensito- 
meter;”  a  so-called  “Matchless”  gas  burner,  by  which  the  gas 
can  be  lowered  out  of  sight  without  entire  extinction ;  this 
will  be  found  vastly  convenient  in  the  dark  room,  Fig.  23. 


The  following  is  a  list  of  chemicals  which  are  certain  to  be 
required  for  development  and  other  operations  with  gelatine- 
bromide  dry  plates : 


Pyrogallol . 1  ounce 

*  Citric  acid . 1  ounce 

Sodic  sulphite,  $  pound  ;  or  potassic  meta  bisulphite.  1  ounce 

Sulphurous  acid . 1  ounce 

Ammonic  or  potassic  bromide . 1  ounce 

*  Liquor  ammonia,  sp.  gr.  .880  (see  later)  . . 4  ounces 

Potassic  carbonate  pure . 4  ounces 

*  Sodic  carbonate  (crystals) . 4  ounces 

f  Sodic  hyposulphite . 1  pound 

*  Potash  alum . 1  pound 

*  Hydrochloric  acid  (comml. ;  useful  for  cleaning  things)  1  pound 

Ammonic  carbonate . 4  ounces 

Mercuric  bichloride  {poison) . 4  ounces 


For  albumen  paper  printing  on  “  ready  sensitized  ”  paper : 

Auric  terchloride  (“  chloride  of  gold,”  in  sealed  tube).  1  tube 
Sodic  acetate,  or  biborate  (“borax”) .  ...  1  ounce 

For  albumen  paper  not  ready  sensitized,  in  addition  to  the 
two  last  items : 


Argentic  nitrate.  . 
Albumenized  paper 


. . . .  1  ounce 
a  few  quires 


60 


PRACTICAL  PHOTOMICROGRAPHY. 


For  printing  on  gelatino-cliloride  emulsion  paper  (“  Aristo- 


type  ”) : 

Ammonic  sulpho-cvanide. . 1  ounce 

Sodic  sulphate . 1  ounce 


For  printing  on  bromide  paper,  transferotype  (Eastman), 


and  for  certain  lantern-slide  plates : 

Ferrous  sulphate  (protosulphate  of  iron) . £  pound 

Potassic  oxalate . 1  pound 

Acetic  acid  (glacial  at  52  deg.  F.) . 1  ounce 

*  Sulphuric  acid,  good  comm’l . 1  ounce 

*  Sodic  chloride  (common  salt) . 1  pound 

Pure  talc  or  “  French  chalk  ”  (for  transferotvye) . 1  ounce 


For  the  wet  plate  collodion  process  either  for  negatives  or 
for  making  lantern  slides,  a  quantity  of  each  of  the  following : 
Collodion  iodized,  or  with  separate  iodizer ;  solution  for  clean¬ 
ing  glass  plates ;  argentic  nitrate ;  f  distilled  or  pure  rain 
water ;  ferrous  sulphate  in  addition  to  the  above,  also  acetic 
acid  or  nitric  acid  ;  sodic  hyposulphite  extra,  or  potassic  cyanide. 

For  all  negative  processes  :  hard  varnish,  5  ounces. 

For  all  lantern  slides  :  cold  “  crystal”  varnish,  5  ounces. 

These  quantities  are  small,  but  will  suffice  for  a  start,  and 
they  are  arranged  as  above  so  that  the  reader  need  not  amass 
a  large  collection  of  chemicals  for  processes  he  does  not  pro¬ 
pose  to  work. 

*  These  may  be  useful  for  all  processes,  and  may  be  stocked  in  larger 
quantity. 

f  Necessary  for  almost  all  processes,  and  may  be  stocked  in  bulk. 


CHAPTER  VIII. 


SOLUTIONS  FOR  PHOTOGRAPHIC  OPERATIONS. 

1st.  To  develop  Gelatine  Bromide  Plates.  The  Pyrogallol 
or  “  Pyro  ”  Solution  : 


Take 

Sodic  Sulphite. 
Water  to  about 


4  ounces  > 
r,  Y  dissolve 

/  ounces  ) 


Make  slightly  acid  with  sulphurous  acid.  Then  pour  into  a 
a  Commercial  one  ounce  bottle  of  Pyro.  Make  up  to  nine 
ounces  and  filter. 

Label  the  bottle  “  Pyro — 10  per  cent.  10  minims==l  grain 
pyro.”  Or  better : 


Take 


Potassic  Meta-Bisulphite* . 34  ounce,  avoir. 

Water  to  about . 7  ounces 


This  will  dissolve  easily,  especially  if  the  salt  is  pounded  ;  then 
pour  into  a  bottle  of  Pyro  as  above  and  label  as  above,  having 
made  up  to  nine  ounces. 

Or,  lastly  :  just  before  using  make  a  sufficient  quantity  of 
water  acid  with  citric  acid,  and  with  that  water  make  a  solu- 
lution  of  four  grains  of  pyro  to  each  ounce  of  acid  water.  This 
will  constitute  one-half  of  the  measure  of  what  will  be  called 
a  “  Normal  Developer.” 

The  writer  uses  and  recommends  the  Potassic  salt  formula. 
But  solutions  known  as  “  Sulpho-Pyrogallol  ”  are  sold,  pre¬ 
pared  more  or  less  according  to  the  formula  of  Mr.  H.  B. 
Berkeley,  the  originator  of  the  compound,  and  these  solutions 
are  usually  good.  As  before,  10  minims  of  the  solution=l 
grain  of  pyro. 


*  A  patent  salt  to  be  obtained  from  The  Scovill  &  Adams  Co. 


62 


PRACTICAL  PHOTO-MICROGRAPHY. 


Alkaline  Solutions. 

Take  1  ounce  (chern.)  Liquor  ammonia  fortiss.  and  dilute  to  10 
ounces  with  water.  (As  soon  as  any  bottle  of  this  solution  of 
ammoniacal  gas  is  opened,  an  equal  bulk  of  water  should  be 
added,  or  better,  water  should  be  added  till  the  hydrometer 
stands  at  .920.)  In  all  cases  the  bottle  must  be  kept  closed  when 
not  in  use,  and  the  stopper  of  the  bottle  should  be  smeared 
with  vaseline.  Of  course,  after  this  dilution  is  effected,  a 
double  quantity  of  the  solution  will  be  required  to  represent 
the  quantity  given  in  terms  of  “  liq.  amm.  fortiss.” 

The  bottle  containing  ten  ounces  (1  oz.  ammonia  and  nine 
of  water)  is  to  be  labelled  :  “  liq.  amm.,  10  per  cent.  1  minim== 
1  minim  ammonia.” 

Or, 

Sodic  Carbonate 
Water  to . . 

Or, 

Potassic  Carbonate 
Water  to . 

Or, 

Sodic  Carbonate . -J  ounce,  avoir 

Potassic  “  . .  Jounce  “ 

Water  to . 9  ounces 

Label :  “  Carb.  10  per  cent. — 10  minims=l  grain  carb.” 

Bromide  Solution. 


Potassic  or  ammonic  bromide .  1  ounce,  avoir 

Water  to .  9  ounces 


Label :  “Bromide  10  per  cent. — 10  minims=l  grain  bromide.” 


Citrate  Solution. 

Sodic  or  potassic  citrate  (or  half  of  each) .  1  ounce,  £^voir 

Water  to . 9  ounces 


Label :  “  Citrate  10  per  cent. — 10  minims=l  grain  citrate.” 

(Note :  If  chemical  weights  be  used,  the  solutions  are  to  be 
made  up  to  10  ounces,  and  labelled  as  above.) 


1  ounce,  avoir 
9  ounces 


1  ounce,  avoir 
9  ounces 


63 


I 

PRACTICAL  PHOTO-MICROGRAPHY. 

Fixing  Solution. 

Sodic  hyposulphite . ..  1  part 

Water .  4  parts  to  5  parts 

Made  decidedly  alkaline  with  a  carbonate  or  with  liq.  amm. 

Clearing  Solution. 


Concentrated  solution  of  potash  alum .  1  pint 

Citric  acid .  3  ounces 

Hydrochloric  acid . . .  2  drams 


If  used  before  fixing  the  acids  should  be  omitted. 

Reducing  Solution.  No.  1.  (Farmer.) 


A.  Potassic  ferricyanide  (red  prussiate  of  potash) . 10  grains 

Water .  1  ounce 

B.  The  ordinary  “  hypo”  solution. 

Reducing  Solution.  No.  2. 


A.  Perchloride  of  iron.  (Druggist’s  tincture  or  satu¬ 


rated  aqueous  sol.) . 2  drams 

Hydrochloric  acid .  4  drams 

Water  to . 20  ounces 


B.  Fresh  hypo,  solution 

(This  is  probably  superior  to  the  Ferricyanide  Reducer  for 
lantern  slides.) 

Intensifying  Solutions. 


a.  Mercuric  bichloride .  1  part 

Water .  20  parts 

Hydrochloric  acid . 5  part 

b.  Sodic  sulphite .  1  part 

Water . . .  .8  to  10  parts 


The  Ferrous  Oxalate  Developer. 

A.  Saturated  solution  at  60  deg.  Fahr.  of  potassic  oxalate, 

B.  1  to  3  aqueous  solution  of  Ferrous  sulphate,  to  each  pint  of  which 

latter  is  added  sulphuric  acid,  1  dram.  (Water  3  parts  ;  Iron  1 
part,  by  weight). 

Notes:  A  “ saturated ”  solution  of  potassic  oxalate  will  hold 
about  1  part  by  weight  of  the  salt  to  4  parts  by  weight  of 
water. 

The  water  may  in  each  case  be  boiled  to  facilitate  solu¬ 
tion.  The  sulphuric  acid  is  to  be  put  into  the  water  before 
the  iron  salt  is  added. 


04 


PRACTICAL  PHOTO-MICROGRAPHY. 


A  and  B  will  keep  a  long  time  if  separate,  but  mixed 
they  will  not  keep.  For  precautions  in  mixing  see  fater. 

Solutions  For  Printing  Processes. 

Sensitizing  Bath  For  Albumenized  Paper. 

Argentic  nitrate . 40  to  65  grains 

Water,  distilled...., . 1  ounce. 

For  the  ammonio-nitrate  process,  and  for  full  instructions 
on  this  entire  subject,  the  reader  is  requested  to  consult  “  The 
Processes  of  Pure  Photography,”  by  Professor  W.  K.  Burton, 
C.  E.,  and  the  present  writer.  (New  York :  The  Scovill  & 
Adams  Co.) 

Toning  Solutions  For  Albumenized  Paper. 


Sodic  acetate . 25  grains 

Auric  chloride  (Terchloride  of  gold) .  1  grain 

Water .  8  ounces 

Used  alkaline. 


Toning  Solution  For  Chloride  Emulsion  Paper. 


See  publication  as  above. 

Fixing  Solution  For  All  Silver  Printing  Processes. 


Hypo. 

Water 


1  i  made  alkaline 

5  parts  ) 


Solutions  For  Platinotype  Printing. 

a.  A  saturated  solution  of  potassic  oxalate.  See  above. 

b.  Hydrochloric  acid,  1  part ;  water,  60  parts. 

c.  The  same  as  b. 


Solutions  for  developing  lantern  slide  plates  of  various 
kinds  will  be  found  under  the  heading  appropriate  to  them  in 
Chap.  XXII  on  lantern  slides. 


CHAPTEK  IX. 


ON  THE  SELECTION  OF  PLATES. 

There  are  not  a  few  able  photo-micrographers  who  assert 
that  the  wet  collodion  process  is  superior  to  the  gelatine 
bromide  process  for  photo-micrography.  The  writer  is  in¬ 
clined  to  dispute  this  point,  on  the  following  grounds :  The 
strongest  argument  of  the  advocates  of  wet  collodion  is  that 
the  deposited  metal  forming  the  image  is  in  the  wet  process 
in  a  finer  state  of  division  than  it  can  be  in  any  gelatine 
process.  The  writer  traverses  this  statement  at  the  outset. 
The  wet  collodion  process  gives  a  more  finely  grained  image 
than  the  rapid  gelatine  emulsion  gives,  certainly ;  but  a  gela¬ 
tine  emulsion  made  with  certain  precautions,  and  suitably  de¬ 
veloped,  yields  a  metallic  image  quite  as  fine  in  grain  as  a 
wet  collodion  image,  if  not  finer.  But  the  gelatine  emulsion 
for  this  must  be  very  “  slow,”  such  as  that  used  for  the  pro¬ 
duction  of  lantern  slides  in  which  the  visible  image  approaches 
a  stain  more  than  a  deposit  in  appearance.  Moreover,  the  de¬ 
posit  in  the  most  sensitive  plate  is  so  fine  as  to  be  incapable  of 
producing  the  slightest  granular  effect  by  direct  contact  print¬ 
ing,  or  even  after  enlargement  of  the  negative  by  photographic 
processes  up  to  at  least  4  diameters.  And  the  writer  is  very 
strongly  of  opinion,  having  worked  and  thought  out  the  mat¬ 
ter  very  carefully,  that  both  in  theory  and  in  practice  no  ad¬ 
vantage  whatever  is  gained,  or  can  be  expected  to  be  gained, 
by  “  camera  enlargement  ”  of  a  negative,  over  a  negative  of 
the  desired  amplification  produced  directly  with  the  micro¬ 
objective.  If,  for  example,  an  ultimate  magnification  of  300 
diameters  is  required,  it  will  be  better  produced  by  direct  am¬ 
plification  by  an  objective  than  by  making  a  negative  at 
“  X  100,”  and  enlarging  3  diameters  in  the  camera ;  and  an 
enlargement  of  3  diameters,  if  properly  managed  will  not, 


66 


PRACTICAL  PHOTO-MICROGRAPHY. 


with  the  coarsest  grained  image  the  writer  ever  saw  produced 
by  gelatine  bromide  emulsion,  show  any  grain  due  to  the 
coarseness  of  the  image  deposit.  We  have,  in  fact,  seen  nega¬ 
tives  in  most  sensitive  gelatine  emulsion  enlarged  5  diameters 
without  the  slightest  appearance  of  grain.  The  argument  for 
the  wet-plate-and-camera-enlargement  is  that  the  ultimate  re¬ 
sult  shows  greater  “  penetrative  ”  effect,  that  is  to  say  that 
there  is  less  apparent  difference  of  sharpness  in  different  planes 
of  the  object;  the  writer  made  a  large  series  of  experiments 
on  diatoms,  enlarging  always  to  X  300,  by  direct  micrographic 
means,  and  by  camera  enlargement  from  original  negatives  at 
100  and  150  diameters ;  in  every  case  the  direct  amplification 
was  superior  to  the  “  enlarged  ”  negative ;  and  the  plates  used 
for  the  100  and  150  diameter  negatives  were  some  wet,  some 
very  slow  gelatine  emulsion,  while  the  negatives  direct  at  300 
were  in  every  case  an  exceedingly  rapid  gelatine  emulsion. 
Thus  much  for  practice,  the  theory  is  too  intricate  to  follow 
here.  At  one  time  the  writer  thought  that  wet  collodion 
would  prove  superior  to  gelatine  emulsion,  and  he  had  got  the 
length  of  producing  a  considerable  number  of  wet  plate  nega¬ 
tives  ;  but  on  using  slow  gelatine  plates  on  the  very  same  sub¬ 
ject,  which  were  chiefly  flies’  tongues,  and  minute  hairs,  he 
found  the  gelatine  results  were  in  every  way  equal  to  the  col¬ 
lodion,  while  the  ease  and  certainty  of  the  former  process 
were  incomparably  greater  than  with  the  latter,  though  the 
writer  is  well  accustomed  to  the  wet  plate  process. 

But  it  is  most  important  to  make  a  wise  selection  of  the  gela¬ 
tine  plates  to  be  used.  Our  objects  may  be  divided  into  two 
great  classes  :  the  coarse  and  the  delicate.  When  our  objects 
are  by  nature  coarse  in  detail,  or  when  they  are  made  actinic¬ 
ally  coarse  by  staining,  we  shall  have  no  difficulty  in  getting 
contrast  in  our  photographs ;  but  when  our  objects  are  very 
minute,  or  composed  of  very  minute  details,  or  when  they  are 
so  stained  as  to  present  very  little  contrast  to  the  background  and 
between  each  other,  the  affair  is  quite  different,  and  a  quite  differ¬ 
ent  class  of  plate  is  required.  Where  the  danger  is  over-contrast 
rather  than  want  of  contrast,  a  “thin  ”  plate,  such  as  is  com¬ 
monly  used  in  portraiture,  is  the  best  to  use ;  but  in  cases  of 


PRACTICAL  PHOTO-MICROGRAPHY. 


67 


great  delicacy  of  detail  or  color — the  real  difficulties  of  photo¬ 
micrography — we  require  a  plate  thickly  coated  with  an  emul¬ 
sion  containing  a  handsome  proportion  of  silver  haloid.  More¬ 
over,  with  the  first  class  of  subject,  over-exposure  is  less  to  be 
feared  than  the  reverse,  so  that  rapidity  of  emulsion  is  rather 
to  be  desired  than  avoided ;  while  with  delicate  subjects  the 
exposure,  even  with  high  powers,  is  never  prolonged  to  incon¬ 
venience,  except  in  very  exceptional  cases  where  oblique  light 
is  used.  A  good  “  portrait  ”  plate,  then,  is  recommended  for 
the  ordinary  run  of  low  power  work,  while  for  the  higher 
flights  of  “  critical  images,”  bacteria  and  the  like,  a  plate 
should  be  thickly  coated,  not  too  rapid,  and  capable  of  giving 
a  plucky,  or  even  a  “  hard,”  negative  at  will. 

The  two  great  factors  in  the  late  advances  in  photo-microg¬ 
raphy  have  been  :  1st.  The  introduction  of  rapid  emulsion ; 
2d.  “  Color  correct,”  or  “  orthochromatic”  photography.  (We 
omit  for  the  present  a  third  factor,  which  is  optical  in  its 
nature).  It  may  be  asserted  that  the  man  who  wishes  to 
produce  photo-micrographs  of  general  utility,  and  still  more, 
he  who  aspires  to  march  anywhere  near  the  van  of  the 
photo-micrographic  army  must  master  orthochromatic  pho¬ 
tography.  There  is  no  getting  round  this  fact.  The  majority 
of  the  most  useful  objects  are  only  to  be  rendered  to  the  best 
advantage  by  color-correct  plates,  and  a  large  number  of  ob¬ 
jects  can  not  be  photographically  rendered  at  all  without  such 
plates ;  and  there  are  objects  which  will  not  be  photographed 
until  orthochromatic  photography  is  perfected.  The  beginner 
should,  therefore,  provide  himself  with  some  orthochromatic 
plates  for  a  start ;  as  he  becomes  accustomed  to  their  manipu¬ 
lation  he  is  advised  to  orthochromatise  his  plates  for  himself, 
if  he  has  facilities  for  drying  plates.  The  subject  of  ortho¬ 
chromatics,  though  far  too  wide,  as  a  whole,  for  full  treatment 
in  this  book,  will  be  treated  as  carefully  and  as  fully  as  the 
author  is  able  to  treat  it  in  a  single  chapter. 

Under  the  heading  of  lantern-slides  we  shall  give  a 
description  of  the  wet  collodion  process,  which  must  suffice  for 
the  reader’s  present  needs  ;  the  process  given  in  that  chapter 
will  serve  to  produce  negatives  as  well  as  positives.  More 


68 


PRACTICAL  PHOTO-MICROGRAPHY. 


complete  instructions  will  be  found  in  “  Processes  of  Pure 
Photography.” 

A  dozen  or  two  of  ordinary  portrait  gelatine  bromide  plates, 
a  dozen  or  two  of  very  slow  thickly-coated  plates,  and  a  dozen 
or  two  of  “  color-sensitive  ”  plates,  will  form  a  sufficient  stock 
for  a  beginner.  If  the  reader  is  au  fait  in  the  wet  collodion 
process,  he  will  do  well  to  try  it  in  order  to  satisfy  himself — as 
the  writer  did — as  to  the  relative  advantages  of  wet  coflodion 
and  dry  gelatine. 

The  greatest  mistake  that  can  be  made  is  to  change  from 
one  make  of  plate  to  another  without  very  weighty  reasons. 
The  beginner,  especially,  should  stick  to  one  make  of  plate 
and  work  with  it  till  he  can  work  it  well.  There  are  few 
plates  in  the  market  that  will  not  yield  a  perfect  negative 
when  properly  used. 


t 


CHAPTER  X. 


THE  CONDENSER  AND  BULL’S-EYE —THEIR  USE 

AND  ABUSE. 

In  some  almost  classical  books  on  the  Microscope,  the  Con¬ 
denser,  Achromatic  or  otherwise,  is  passed  over  with  little  more 
than  mere  mention  ;  its  construction  is  described  en  passant, 
but  it  is  easy  to  see  that  the  writers  placed  little  importance  on, 
even  if  they  understood,  its  use.  It  is  by  no  means  a  long 
time  since  even  the  best  microscopists  were  not  wholly  aware 
of  the  full  advantage  to  be  gained  by  a  proper  use  of  the  con¬ 
denser,  and  the  author  is  informed  that  Mr.  E.  M.  Nelson 
played  a  prominent  part  among  the  demonstrators  of  the 
scientific  application  of  what  is  now  admitted  on  all  hands  to 
be  a  matter  almost  as  important  as  the  objective  itself. 

The  condenser,  as  before  stated,  is  not  intended  merely  to 
throw  a  blaze  of  light  upon  the  object,  and  as  it  is  necessary 
that  the  photo-micrographer  should  thoroughly  understand  the 
use  of  the  condenser  a  diagram  and  some  remarks  are  here 
given,  which,  it  is  hoped,  will  elucidate  the  matter,  and  still 
further  remarks  and  diagrams  will  be  found  in  a  later  chapter. 
(See  p.  83) 


Fig.  25. — General  Outline  of  Elements  of  a  Condenser. 


The  substage  condenser  is  made  to  collect  the  pencils  of 
light  from  the  radiant  H,  and  to  focus  these  pencils  on  the 


f 


70  PRACTICAL  PHOTO-MICROGRAPHY. 

object  0.  The  object-glass  is  also  made  to  focus  on  O  ;  and 
object-glass  and  condenser  are  working  at  their  best  when  the 
object,  or  the  critical  plane  of  the  object,  lies  in  focus  of  both 
object-glass  and  condenser,  and  then  only.  The  best  resolution 
of  any  plane  of  an  object  can  only  be  achieved  when  the 
object  lies  in  the  conjugate  foci  of  objective,  and  condenser. 
But  the  focus  of  the  condenser  is  not  usually  long  enough  to 
throw  upon  the  object  an  image  of  the  light  large  enough 
to  cover  evenly  the  field  of  the  objective  and  so  with  low 
powers  we  have  an  image  of  the  light  only  partially  cover¬ 
ing  our  field,  and  while  scientifically  speaking  this  is  the 
true  critical  image  of  our  object,  still,  as  a  rule,  a  photo¬ 
graph  of  an  image  so  illuminated  would  be  unsightly.  There¬ 
fore  we  make  a  compromise  in  one  of  several  ways  ;  we 
sacrifice  to  some  extent  the  accuracy  of  our  critical  image  in 
order  to  make  a  more  sightly  photograph.  And  often  we  may 
have  so  much  resolving  power  “  in  hand,”  so  to  speak,  that 
we  may  sacrifice  some  of  it  without  losing  any  of  the  necessary 
resolution.  Be  it  clearly  understood  that  a  critical  image  is 
really  the  image  of  the  radiant  with  the  object  intercepting 
certain  pencils  of  light ;  this  is  fact  for  all  cases  of  axial  trans¬ 
mitted  light,  but  there  are  cases  of  oblique  lighting  and  reflected 
lighting  where  the  object  itself  becomes  the  radiant.  At  pres¬ 
ent  we  deal  only  with  axial  transmitted  light. 

We  effect  the  compromise  mentioned  above  in  various  ways,, 
some  better  than  others.  The  commonest  way  is  to  interpolate 
between  light  and  condenser  a  bull’s-eye  which  collects  pencils 
of  light  from  the  radiant  and  transmits  them  parallel  to  each 
other  into  the  condenser.  The  result  of  this  is  that  the  rays 
previously  focused  on  a  small  area  of  the  object  are  now  spread 
evenly  over  the  whole  field,  and  if  the  bull’s-eye  is  properly  used 
in  such  a  case  there  ought  to  be  no  falling  off  in  the  quality  of 
the  image.  It  is  important  to  keep  the  bull’s-eye  at  a  good 
distance  from  the  condenser,  and  the  radiant  must  be  at  the 
focal  point  of  the  bull’s-eye.  This  is  the  usual  method  of 
procedure  with  simple  objects  and  low  powers.  The  bull’s- 
eye  is  sometimes  used  alone  as  a  condenser,  being  turned  with 
its  convex  side  toward  the  radiant,  and  where  an  angle  of  not 


PRACTICAL  PHOTO-MICROGRAPHY. 


71 


more  than  125  deg.  is  required,  it  answers  fairly  well  in  this 
capacity. 

Another  method  of  compromising  has  been  much  used  by 
the  writer  for  very  low  power  work,  and  even  under  certain 
circumstances,  for  high  power  work  ;  it  answers  as  a  makeshift 
for  the  low  power  work,  bnt  is  not  recommended  for  high 
power  where,  in  fact,  it  is  not  necessary.  The  arrangement  is 
shown  in  figure  26. 


G  B 


Fig.  26. 


Here  R  is  the  radiant,  B  a  bull’s  eye  parallelizing  R’ s  rays 
upon  a  disc  of  very  finely  ground  glass  G,  the  bull’s  eye  and 
disc  being  so  fitted  that  they  can  be  fixed  as  a  whole  piece  of 
apparatus,  in  front  of  the  radiant.  Reference  to  figure  16  will 
explain  the  fitting  of  this  to  the  front  of  the  lantern ;  S,  in 
figure  26,  being  a  pinch  screw  by  which  the  apparatus  is  fast¬ 
ened  to  the  front.  Here  G  becomes  practically  the  radiant, 
and  the  writer  hoped  great  things  for  this  arrangement,  until 
he  found  that  he  could  not  accurately  focus  the  ground  glass, 
even  when  oiled,  on  his  object  without  getting  an  image  of  the 
grain  of  the  ground  glass,  which  was  fatal,  of  course,  to  accurate 
focussing  of  this  radiant.  But  for  the  lowest  power  work,  where 
the  angular  aperture  of  the  objective  (as  3-inch,  4-inch,  etc.)  is 
very  low,  and  where  the  use  of  a  condenser  is  forbidden,  this 
apparatus  is  strongly  recommended  and  often  used  by  the 
writer.  It  might  appear  that  by  using,  in  place  of  the  piano 
convex  B,  a  double  convex,  a  small  disc  of  very  brilliant  light 
would  be  obtained  on  G,  the  size  regulated  by  sliding  G  to 
and  from  B 3  and  that  this  small  disc  would  be  very  valuable 


72 


PEACTICAL  PHOTO-MICEOGEAPHY. 


for  medium  and  high  power  work ;  but  it  is  not  so,  for  the  diffi¬ 
culty  of  focusing  the  image  of  the  ground  glass  again  comes  in. 
It  may  be  worth  while  to  try,  in  place  of  ground  glass  at  O,  a  cell 
full  of  milk  and  water,  as  suggested  by  a  friend  of  the  writer. 

There  is  still  another  method  of  obtaining,  with  a  condenser 
alone,  an  evenly  lighted  field.  This  method  consists  in  mis- 
focusing  the  condenser,  but  we  need  hardly  point  out  at  any 
great  length  the  danger  of  this  system.  If,  in  Fig.  27,  A  be 
the  object  and  C  the  condenser  focused  on  A,  as  shown  by 


continuous  lines,  the  image  of  the  light  seen  with  a  low-power 
objective  may  be  too  small  to  cover  the  field  ;  if  we  focus  the 
condenser  down  (dotted  lines),  or  up  (interrupted  lines),  we 
shall  get  an  even  field  of  light,  but  our  object  will  no  longer 
fulfill  our  condition  of  being  in  the  foci  of  condenser  and 
objective  at  once,  and  so  our  image  will  be  inferior.  If  we 
focus  our  condenser  and  o.  g.  both  on  our  object,  look  down 
the  tube  without  ocular,  arrange  our  condenser  aperture  so  as 
to  file  our  o.  g.  with  light,  and  then  rack  down  our  condenser, 
we  shall  see  that  our  o.  g.  is  no  longer  fully  utilized ;  but  on 
replacing  the  ocular  we  may  find  our  field  now  evenly  lighted. 
So  that  focusing  down  our  condenser  has  entailed  loss  of 
aperture.  If,  by  opening  our  condenser  aperture  by  an  iris 
or  by  a  larger  stop  we  can  once  more  fill  our  objective  with 
light,  probably  not  much  harm  will  be  done  to  the  quality  of 
image  by  our  racking  down  of  the  condenser ;  still  the  writer 
decidedly  objects  in  practice  to  this  system  of  mis-focusing, 
and  recommends  any  other  system  in  preference  to  this  one. 

To  recapitulate :  W  ith  low  powers,  where  the  image  of  the 
radient  focused  on  the  object  does  not  sufficiently  fill  the  field, 


PRACTICAL  PHOTO-MICROGRAPHY. 


73 


a  bull’s-eye  may  be  placed  between  light  and  condenser,  at  a 
possible  sacrifice.  With  high  power  objectives  the  image  of 
the  flame,  focused  as  before,  is  usually  large  enough  to  illu¬ 
minate  the  whole  field  without  any  bull’s  eye.  With  the  low¬ 
est  powers  the  condenser  is  usually  and  preferably  omitted. 

.Note. — In  very  many  cases  it  will  be  found  convenient  and 
advantageous  to  use  an  objective  as  substage  condenser.  The 
objective  so  used  may  have  an  aperture  equal  to  or  less  than 
that  of  the  objective  used  for  the'  image  projection.  Those 
who  have  good  objectives,  but  only  poor  condensers,  may  do 
well  to  adopt  this  system  for  all  work.  The  writer,  for  pur¬ 
pose  of  experiment,  had  a  mount  made  fitting  his  substage  and 
taking  his  objectives ;  the  addition  of  a  small  iris  diaphragm 
made  the  apparatus  complete.  The  results  were  so  satisfactory 
that  we  would  not  hesitate  to  adopt  this  system  entirely,  were 
we  not  already  in  possession  of  Powell  and  Lealand’s  fine  apo- 
chromatic,  and  Zeiss’  achromatic  condensers ;  the  former  of 
N.  A.  1-4,  the  latter  of  N.  A.  1,  and  capable  of  being  used  for 
quite  low  angles.  For  example,  using  in  our  substage  as  con¬ 
denser  an  apochromatic  o.  g.  of  16  mm.  N.  A.  .30,  we  resolved 
with  a  2  mm.  o.  g.  P.  angulatum,  into  white  areas  or  black  dots, 
with  ease  and  at  will.  For  ordinary  photography  of  bacteria 
and  the  like  we  find  this  arrangement,  or  a  similar  one,  not  at 
all  inferior  to  the  use  of  expensive  achromatic  condensers. 


CHAPTER  XI. 


THE  USE  OF  THE  EYE-PIECE  OR  OCULAR. — STOPS. — 

REFLECTIONS. 

The  ocular  in  ordinary  microscopy  is  an  optical  system 
whereby  the  aerial  image  produced  by  the  objective  is  “  taken 
up  ”  and  projected,  magnified  more  or  less,  on  the  retina  of 
the  human  eye.  The  ordinary  Huyghenian  ocular  is  made 
for  this  sole  purpose ;  it  is  frequently  made  non-achromatic 
It  is  therefore  not  to  be  expected  that  an  ordinary  Huyghen¬ 
ian  ocular,  particularly  one  not  achromatized,  should  project 
a  perfect,  or  even  a  good  image  on  a  flat  plate  perhaps  30 
inches  distant  from  the  spot  for  which  the  ocular  was  intended 
to  work.  The  writer  is,  however,  bound  to  accept  as  a  fact  in 
the  experience  of  others  what  his  own  experiments  have  in¬ 
variably  failed  to  verify,  viz. :  that  in  some  cases  an  ordinary 
microscope  ocular  does  project  on  a  screen,  distant  from 
the  ocular  from  20  to  40  inches,  a  true  image,  and  that  a 
photograph  tolerably  faithful  to  nature  can  be  made  of  that 
projected  image  in  the  usual  way.  Certainly  it  is  conceivable 
that  by  some  accidental  suitability  of  ocular  to  objective  such 
a  result  may  be  obtained.  The  writer,  therefore,  does  not 
gainsay  the  assertion  that  photo-micrograplis  of  the  highest 
quality  and  of  difficult  objects  may  be  produced  by  the  use  of 
the  ordinary  achromatic  eye-piece,  but  he  does  say  that  he  has 
never  produced  nor  ever  seen  any  photo-micrographs  that  he 
could  call  first-rate  obtained  by  the  use  of  the  common  eye¬ 
piece  sold  with  ordinary  microscopes  and  used  for  ordinary 
observation.  On  the  other  hand  microscopic  objectives  are 
not  intended  for  projecting  images  upon  screens  several  feet 
distant,  but  are  constructed  so  that  their  best  image  falls 
somewhere  between  6  and  12  inches  up  to  the  microscope 
tube ;  and,  moreover,  that  image  is  intended  to  be  “  picked 


PRACTICAL  PHOTO-MICROGRAPHY. 


75 


up”  carried  on,  modified,  and  in  many  cases  and  ways  cor¬ 
rected  by  an  ocular.  Still  the  author  has  seen  and  produced 
micrographs  without  an  ocular  not  easily  to  be  surpassed. 

One  of  the  latest  outcomes  of  optical  science  has  been  the 
construction  by  Herr  Zeiss,  of  Jena,  on  formulae  by  Dr.  Abbe, 
of  a  series  of  oculars  arranged  for  the  purpose  of  projecting 
the  image  formed  by  the  objective.  The  writer  may  as  well 
state  at  once  that  he  believes,  and  has  good  reason  to  believe, 
that  in  the  use  of  the  projection  oculars,  with  other  matters  of 
different  nature,  will  lie  the  future  of  scientific  photo-micro¬ 
graphy.  In  the  author’s  experience  these  oculars  have  acted 
well  with  objectives  made  by  makers  other  than  Zeiss ;  for  in¬ 
stance,  they  have  been  found  to  work  satisfactorily  with  a 
1-inch,  a  and  a  y1^  immersion,  all  by  Swift  of  London  ;  also 
fairly  well  with  a  by  Reichert.  It  is  matter  for  congratu¬ 
lation  that  the  Zeiss  (or  Abbe)  projection  oculars  are  cheap, 
costing  only  about  £2,  or  say  $10  each.  A  chapter  will 
be  devoted  to  the  apochromatic  lenses  and  “  compensating  ” 
and  “  projection  ”  oculars  made  by  Zeiss. 

Undoubtedly  an  eye-piece  of  any  kind,  when  it  can  be  used 
without  detriment  to  result,  is  a  great  convenience.  The  cam¬ 
era  does  not  require  to  be  so  long ;  there  is  less  danger  of 
internal  reflections,  which  must  be  sedulously  avoided,  as  will 
presently  be  seen.  But  failing  a  projection  ocular,  or  failiug 
the  necessary  coincidence  between  projection  ocular  and  ob¬ 
jective,  the  balance  of  opinion  and  the  balance  of  high-class 
results  are  probably  in  favor  of  the  image  projected  directly 
upon  the  screen  by  the  objective.  The  writer  at  all  events  is 
willing  to  commit  himself  to  this  opinion,  and  to  recommend 
either  a  projection  ocular  or  none. 

Amount  of  Magnification.  To  discuss  this  question  w'e  may 
adopt  an  arbitrary  term:  “Initial  power.”  We  propose  to 
call  the  initial  power  of  an  objective  the  amount  of  magnifica¬ 
tion  (in  terms  of  diameters)  given  by  the  objective  at  10  inches 
behind  its  posterior  conjugate  focus.  (The  distance,  10  inches, 
is  about  the  distance  for  distinct  normal  vision,  and  is  chosen 
for  that  reason.)  A  good  objective  will,  as  a  rule,  when  properly 
used,  stand  a  strain  of  magnification  to  ten  times  its  initial  power. 


76 


PRACTICAL  PHOTOMICROGRAPHY. 


Thus  :  A  lens  of  one  inch  focus  gives  at  about  10  inches  up  the 
tube  a  magnification  of  10  diameters ;  by  whatever  means  we  try 
to  get  from  that  lens  a  magnification  of  100  diameters  projected 
as  a  real  image,  it  must  be  a  good  lens  if  it  stands  that  strain  with¬ 
out  breaking  down  in  definition  or  corrections.  In  fact  none  but 
the  very  best  objectives  will  tolerate  any  such  strain.  By  dint  of 
exceedingly  skillful  manipulation  such  as  only  a  few  men  can 
claim  to  have  acquired,  we  have  known  specially  fine  objectives 
stand  a  stretch  of  their  powers  even  greater  than  this,  but  the 
writer’s  own  attempts  in  this  direction  have  always  been  utter 
failures,  and  in  the  majority  of  cases  six  or  seven  times  the 
initial  power  is  ample  to  produce  a  faltering  of  the  lens’ 
capabilities.  And  this  holds  good  whatever  be  the  means 
adopted  for  increasing  the  magnifying  power  of  the  objective, 
whether  long  stretch  of  camera  or  high  eye-piecing,  or  the  two 
combined.  Thus  Zeiss  makes  two  projection  oculars  for  one 
series  of  lenses ;  the  first  ocular  increases  the  magnification  by 
“  three  times  ”  and  may  be  used  without  difficulty  up  to  a 
stretch  of  about  30  inches  from  ocular  to  sensitive  plate  (giving 
a  power  about  nine  times  the  “  initial  power  ”)  ;  while  the 
higher  power  projection  ocular  magnifying  “  six  times  ”  will 
at  the  same  stretch  break  down  the  finest  objectives,  unless  the 
skill  of  the  operator  be  very  great  indeed,  greater  than  the 
writer  can  claim,  certainly. 

“ Stopping  down”  Objectives.  It  is  common  to  find  at  the 
back  of  objectives  a  cell  or  diaphragm  constricting  more  or 
less  the  light-way  from  the  objective  to  the  eye  or  to  the  plate. 
So  long  as  the  “  stops  ”  do  not  cut  off  any  pencils  of  light  that 
otherwise  would  reach  the  plate  or  the  retina  no  harm  is  done ; 
but  if  the  stops  are  used  as  a  supposed  means  of  reducing 
aberrations  or  incorrectnesses  of  the  objective,  a  great  deal 
of  harm  is  done  and  a  very  foolish  mistake  made.  By  the 
time  that  the  pencils  of  light  have  passed  through  the  objective 
the  mischief  is  done,  if  it  is  done  at  all,  and  a  stop  behind 
the  objective  may  hide ,  but  cannot  possibly  correct  any 
errors.  Whatever  “  stopping  ”  is  to  be  done  should  be  done 
in  front  of  the  objective,  that  is  to  say  in  the  condenser,  or, 
failing  a  condenser,  in  the  substage.  If,  therefore,  the  reader 


PRACTICAL  PHOTO-MICROGRAPHY. 


77 

finds  a  stop  at  the  back  of  any  objective,  the  aperture  being 
small  enough  to  constrict  to  any  notable  extent  the  cone  of 
rays  proceeding  from  the  objective,  he  is  advised  to  remove 
that  cell  or  stop,  blackening  with  some  dead-black  pigment  the 
interior  of  the  objective  where  it  will  probably  be  found  bright. 
The  writer  owns  a  ^-inch  o.g.  which,  when  purchased,  had  a 
ridiculously  small  stop  at  the  back.  The  lens  was  condemned 
as  very  poor  by  several  experts  who  examined  it  ;  but,  on  re¬ 
moval  of  the  stop  by  way  of  experiment,  it  was  found  to  be 
a  very  good  lens  indeed,  and  has  been  much  used  by  the  writer 
for  a  certain  class  of  work. 

Reflections  inside  the  apparatus.  The  reader  is  earnestly 
advised  to  made  sure  that  there  are  no  “  shiny  ”  points  or  sur¬ 
faces  inside  any  part  of  his  apparatus  for  photo-micrography. 
The  inside  of  a  microscope  tube  is  almost  invariably  worn 
bright  at  some  places,  and  even  the  black  varnish  inside  an 
ordinary  camera  is  often  quite  capable  of  causing  most  trouble¬ 
some  “flares.”  The  micro-tube  should  be  lined  with  black 
velvet,  and  not  only  should  the  interior  of  the  camera  be 
dead  black  all  over,  but  blackened  cards  should  be  put  inside, 
having  apertures  graduated  from  front  to  rear  of  the  appa¬ 
ratus,  so  that  no  light  can  reach  the  plate  except  that  which 
passes  through  the  objective  and  forms  the  image  on  the  plate. 
This  is  a  most  important  caution  and  is  especially  to  be  ob¬ 
served  when  the  image  is  projected  by  the  objective  alone 
without  ocular,  for  as  already  noted  the  ocular  has  the  merit 
of  reducing  danger  from  untoward  reflections.  Whether  the 
ocular  is  in  use  or  not  there  should  always  be,  as  close  as  con¬ 
venient  to  the  front  of  the  sensitive  plate,  an  opaque  plaque 
having  a  disc  of  aperture  a  shade  larger  than  the  area  of  plate 
being  used.  Th v  plaques  may  be  of  cardboard,  wood,  metal, 
or  any  other  suitable  material,  but  they  must  present  a  dead- 
black  surface. 

Sometimes  the  edges  of  the  apertures  in  the  condenser-stop 
become  bright  from  friction,  and  this  is  specially  the  case  with 
badly  designed  “  Iris  ”  diaphragms.  The  writer  has  had  con¬ 
siderable  trouble  with  this  defect  in  one  of  his  apparatus,  and 
warns  the  reader  against  it.  Internal  reflections  cause  uneven 


* 


78 


PRACTICAL  PHOTO-MICROGRAPHY. 


illumination,  “flares,”  and  poor  thin  negatives  with  back¬ 
grounds  dirty  grey  in  place  of  dense  black. 

The  apartment  where  microscopic  work,  visual  or  photo¬ 
graphic,  is  going  on,  should  be  as  nearly  dark  as  possible. 


' 


I 


No.  2.— Triceratium,  X  750. 


Plate  II 


CHAPTER  XII. 


PROGRESSIVE  EXAMPLES. 

It  is  proposed  in  this  chapter  to  give  a  few  examples  of 
operations  for  subjects  presenting  various  degrees  of  difficulty  ; 
taking  to  start  with  the  easiest  class  of  object  likely  to  be  met 
with,  and  attacking  it  with  the  simplest  apparatus  likely  to  be 
required  for  any  class  of  work. 

Example  1.  A  subject  presenting  only  light-obstruction, with¬ 
out  very  delicate  marks  or  structure,  and  with  just  enough  of 
color  to  give  actinic  contrast,  thin  and  flat ;  to  be  photographed 
with  a  low  power  to  a  magnification  not  exceeding  20  diame¬ 
ters;  no  ocular  nor  condenser,  direct  illumination.  Subject; 
a  good  section  of  wood.  Objective :  two  inches  focus  or  lower 
power.  If  an  oil  lamp  provide  the  illumination  the  wick  to 
be  turned  “  broadside  on.” 

Procedure :  Having  focused  the  object  with  objective  and 
ordinary  ocular,  arrange  the  object  and  light  carefully  so  that 
the  whole  field  is  evenly  illuminated ;  attach  the  camera  to 
the  microscope,  the  ocular  being  entirely  removed.  Proceed 
to  adjust  the  focus  on  the  ground-glass  of  the  camera ;  for  this 
the  microscope  tube  will  require  more  or  less  racking  in.  In 
such  work  as  this  there  is  danger  of  the  tube  cutting  off  part 
of  the  field ;  a  good  wide  tube  is  therefore  an  advantage. 
Notes :  It  is  supposed  that  the  reader  has  studied  the  foregoing 
instructions  and  diagrams  with  regard  to  means  for  preventing 
access  of  stray  and  reflected  light  to  the  sensitive  plate.  The 
leather  cap  seen  at  No.  11,  on  Fig.  16,  is  in  the  writer’s  prac¬ 
tice  placed  on  the  end  of  the  tube,  and  the  camera  is  then 
pushed  forward  till  the  brass  cap  on  the  front  passes  into 
the  leather  cap  11,  thus  forming  a  light-tight  junction. 

In  order  to  make  sure  that  the  lighting  of  the  field  is  even, 
the  best  plan  is  to  remove  the  ground-glass  of  the  camera,  and 


80 


PRACTICAL  PHOTO-MICROGRAPHY. 


to  hold  a  few  inches  behind  its  late  position  a  piece  of  white 
paper  or  cardboard.  On  this  white  surface  the  image  is  visibly 
projected,  and  uneven  lighting  easily  detected. 

In  most  cases  the  ground  glass  of  the  camera  and  the 
coarse  adjustment  of  the  microscope  permit  of  sufficiently 
accurate  focusing  with  very  low  powers,  but  a  “  Ramsden  ” 
eye-piece  placed  on  the  plain  glass  focus-screen  may  be  found 
preferable  in  conjunction  with  the  fine  adjustment  of  the 
microscope.  Often,  however,  where  a  good  general  appearance 
is  wanted  the  unaided  eye  and  ground  glass  are  better  in 
practice. 

Our  ground-glass  disc  illuminated  by  parallelized  rays,  as 
figured  ISTo.  26  on  page  71  will  be  found  most  convenient  for 
this  class  of  work. 

While  the  object  is  being  examined  in  the  microscope  with 
the  ocular,  the  part  of  the  object  occupying  the  centre  of  the 
field  should  be  carefully  noted ;  this  point  must  occupy  pre¬ 
cisely  the  centre  of  the  ground-glass,  where  the  camera  is 
attached.  If  the  apparatus  is  of  the  construction  suggested  on 
page  51,  where  the  microscope  and  the  light  are  fixed  in  their 
relationship  to  each  other,  and  where  the  table  bearing  them 
rotates  to  a  “  stop  ”  when  the  camera  is  about  to  be  attached, 
it  is  important  to  note  at  the  very  first  whether  the  centre  of 
the  object  coincides  precisely  with  the  centre  of  the  ground- 
glass  when  the  image  is  seen  on  the  ground-glass.  The  centre 
of  the  latter  should  be  marked  in  pencil  on  the  ground  side  of 
the  glass  ;  this  may  be  done  by  drawing  diagonals  and  describ¬ 
ing  a  little  circle  round  the  intersection  of  the  diagonals.  The 
cardboard  or  other  discs  recommended  on  page  77,  should  have 
apertures  corresponding  in  size  to  the  sizes  of  plates  to  be  used. 

These  remarks  if  carefully  noted  and  acted  upon  will  save 
trouble  in  future,  and  the  image  being  focused  on  the  ground- 
glass,  the  dark  slide  carrying  the  sensitive  plate  is  inserted  in 
its  place,  the  light  shut  off,  preferably  by  a  shutter  working 
very  easily  inside  the  camera,  and  all  is  ready  for  exposure, 
remarks  on  which  are  left  for  a  later  page. 

Example  No.  2.  A  subject  similar  to  No.  1,  but  more  finely 
marked  and  smaller,  requiring  more  angular  aperture,  and  still 


PRACTICAL  PHOTO-MICROGRAPHY. 


81 


practically  colorless.  Low  power,  narrow  angle  condenser 
magnification  about  30  diams.  without  ocular,  120  with  pro¬ 
jection  ocular.  Subject  a  flat  diatom  as  Arachnoidiscus 
Ehrenbergii ,  or  an  Echinus  Spine.  Objective  two-thirds  inch 
or  one  inch  ;  Achromatic  condenser,  front  hemisphere  removed. 

Procedure :  A.  To  centre  the  condenser — ( this  step  must 
be  taken  in  every  case  when  a  substage  condenser  is  to  be  used.) 
Placing  the  pinhole  cap  on,  or  a  pinhole  diaphragm  in,  the 
condenser,  examine  with  a  low  power  objective  and  eye  piece, 
working  the  substage  centering  screws,  till  the-  disc  of  light, 
(which  may  proceed  from  any  radiant),  occupies  precisely  the 
centre  of  the  field.  Remove  pinhole  stop  or  cap. 

B.  To  centre  the  light.  ( This  also  must  be  performed  in 
every  case.)  The  condenser  being  centred  as  under  “  A,”  rack 
out  and  in  the  substage  and  the  microscope  tube  with  objective 
and  low  power  eye-piece,  until  an  image  of  the  light  is  seen 
sharp  in  some  part  of  the  field.  (The  light  may  require  to  be 
moved  in  order  to  bring  it  upon  the  field.)  'With  an  oil  lamp 
the  wick  should  present  its  edge  to  the  condenser.  Move  the 
light  from  side  to  side  and  up  and  down  till  its  image  falls 
directly  in  the  centre  of  the  field. 

G.  To  focus  objective  and  condenser  on  the  object.  Place 
the  object  on  the  stage  so  that  it  occupies  the  central  position, 
focus  the  objective  on  the  object  and  then  rack  the  substage 
till  the  image  of  the  light  is  sharply  focused  across  the  object. 
This  is  a  suitable  arrangement  so  far  for  obtaining  the  best 
possible  image  microscopically  of  a  certain  area  and  plane  of 
the  object.  The  nearer  the  light  is  to  the  substage,  and  the 
longer  the  focus  of  the  condenser,  the  larger  will  be  the  sharp 
image  of  the  radiant  across  the  object. 

D.  To  spread  the  light  evenly  over  the  field  either  a  bull’s- 
eye  or  a  diffusing  medium — as  the  ground-glass  referred  to 
above — must  be  placed  between  the  light  and  the  condenser. 
If  the  “  ground-glass  and  bull’s-eye  ”  arrangement  be  used,  the 
result  is  simply  to  transfer  the  radiant  surface  from  the  lamp  to 
the  ground-glass  ;  if  the  bull’s-eye  alone  be  used  the  result  is  to 
fill  the  back  of  the  condenser  with  parallel  rays ;  and  in  order 
to  get  the  most  evenly  lighted  field  the  condenser  will  probably 


82 


PRACTICAL  PHOTO-MICROGRAPHY. 


require  to  be  racked  down  more  or  less.  The  use  of  the  bull’s- 
eye  is  so  important  that  diagrams  and  quotations  from  papers 
by  Mr.  E.  M.  Nelson,  in  the  English  Mechanic ,  1884,  shall  be 
given  in  explanation.  In  the  first  place  the  light  must  be  in 
the  focus  of  the  bull’s-eye,  and  the  latter  is  to  be  fixed  so  that 
the  edge  of  the  flame  if  a  wick  is  used,  or  the  surface  of  the 
lime  if  the  limelight  is  used,  is  in  the  focus  of  the  bull’s-eye. 
In  order  to  ascertain  whether  the  bull’s-eye  and  light  are  in 
proper  relation  to  each  other,  Mr.  Nelson  recommends  either 
that  the  eye  be  placed  in  the  rays  proceeding  from  the  bull’s- 
eye,  or  that  a  condensing  lens  be  placed  in  the  rays  and  the 
image  thrown  upon  a  white  card  there  examined. 

In  fig.  28,  E  represents  the  edge  of  the  flame,  P  the  bull’s- 
eye  and  A  the  image  as  it  ought  to  be  seen  on  the  card. 


P 


C  D 

©  O  «> 

Fig.  28. 

B  represents  the  appearance  when  the  bull’s  eye  is  too  near 
the  edge  of  the  flame. 

C  represents  the  appearance  when  the  bull’s  eye  is  too  far 
away  from  the  flame. 

D  shows  the  appearance  when  the  bull’s  eye  is  focused,  but 
out  of  centre. 

In  order  to  get  the  proper  use  of  the  bull’s-eye,  it  should  not 
be  nearer  to  the  substage  than  a  distance  of,  say,  12  inches. 

The  same  papers  by  Mr.  N  elson  contain  information  regard¬ 
ing  the  substage  condenser,  so  useful  that  the  author  ventures 
to  copy  some  further  figures. 


PRACTICAL  PHOTO-MICROGRAPHY. 


83 


A  (Fig.  29)  shows  a  substage  condenser  and  an  objective 
focused  on  the  same  point,  and  the  aperture  of  both  equal  and 
fully  utilized.  On  looking  down  the  microscope  tube  the  lens 
will  be  seen  filled  with  light  as  at  C. 

B  shows  a  condenser  and  an  objective  still  focused  on  one 
point,  but  having  their  apertures  cut  down  by  a  stop  in  the 
condenser  ;  the  back  lens,  examined  as  before,  will  present  the 
appearance  of  D. 


Fig.  29. 


These  remarks  and  quotations,  though,  perhaps,  not  in  their 
proper  order  here,  are  to  be  specially  noted  in  every  case  where 
a  bull’s-eye  is  used.  The  bull’s-eye,  as  already  stated,  should 
be  on  a  stand  with  a  heavy  base,  and  in  order  to  focus  the  con¬ 
denser  when  the  bull’s-eye  is  to  be  used,  the  following  steps 
may  be  taken.  The  objective  being  focused,  the  condenser 
and  light  centered,  the  edge  of  the  bull’s-eye  is  advanced  in 
front  of  the  light  and  the  image  of  the  metal  rim  of  the  bull’s- 
eye  is  focused  on  the  object  by  means  of  the  condenser.  At 
the  same  time  the  worker  must  take  care  that  the  segment  of 


84 


PRACTICAL  PHOTO-MICROGRAPHY. 


the  circle  of  the  bull’s-eye  seen  on  his  field  is  vertically  central, 
i.  e.,  the  imaginary  centres  of  bull’s-eye  and  field  should  be  in 
one  line.  This  is  difficult  to  explain,  but  will  be  understood 
on  experiment.  Lastly,  when  the  field  is  illuminated,  the 
bull’s-eye  being  focused  and  in  its  place  centrally,  the  worker 
is  to  look  down  his  tube  and  compare  what  he  sees  with  our 
figures  on  pages  82  and  83.  If  the  entire  area  of  the  back 
combination  is  filled  with  light,  we  are  utilizing  all  the  aper¬ 
ture  of  our  objective,  and  it  may  be  said  that,  in  many  cases 
where  it  is  desirable  to  utilize  every  fraction  of  aperture  that 
our  objective  possesses,  the  use  of  the  bull’s-eye  is  to  be  recom¬ 
mended.  In  many  cases  the  use  of  our  entire  aperture  intro¬ 
duces  photographic  difficulties,  but  these  must  be  overcome. 
If  a  photograph  is  wanted  of  the  “  general  appearance  ” 
of  an  object,  it  is  well  to  cut  down  the  aperture  much  more 
than  would  be  permissible  where  a  scientific  photographic 
representation  is  required.^  We  are  aware  that  this  is  heresy 
to  some  old  workers. 

Example  Ho.  3. — A  “  critical  image,”  with  a  low  power,  a 
condenser,  no  bull’s  eye.  Subject :  “  Test  hairs  ”  on  a  blow¬ 
fly’s  proboscis.  Objective:  A  two-thirds,  one-half,  or  one- 
quarter  inch  of  highest  attainable  aperture  ;  this  test  for  a  one- 
quarter  inch  being,  as  a  rule,  too  easy.  Projection  ocular 
used ;  magnification  from  150  to  400  diameters.  See  Plate  I, 
fig.  1. 

A  and  B,  centre  condenser  and  light  as  before.  C,  for  the 
two-thirds,  or  one-half,  or  four-tenths  objective,  the  substage 
condenser  may  be  usod  without  its  front  hemisphere,  unless 
with  its  front  it  has  a  very  low  angle,  or  unless  it  is  not  achro¬ 
matic.  Two  things  must  always  be  observed  with  regard  to 
the  condenser ;  first,  it  must  have  sufficient  angle  to  fill  the 
objective ;  second,  whatever  its  angle  be,  if  its  angle  is  greater 
than  that  of  the  objective,  it  must  be  stopped  down  till  the 
angles  are  nearly  equal.  This  time  the  object  is  focused  care¬ 
fully  with  the  objective,  and  then  the  light  is  most  carefully 
focused  on  the  part  of  the  “  tongue  ”  to  be  photographed.  The 
hairs  will  now  be  seen  more  or  less  elongated,  according  as  the 
correction  of  the  objective  happens  to  be  more  or  less  accurate. 


PRACTICAL  PHOTO-MICROGRAPHY. 


85 


Now  come  in  the  skill  and  experience  of  the  worker,  for  the 
objective  has  now  to  be  corrected  for  the  thickness  of  the 
cover  glass  and  the  position  of  the  test  hairs  with  regard  to  the 
cover  glass.  The  correction  is  to  be  accomplished  by  means 
of  “  screw  collar,”  if  the  objective  has  one,  or  by  length  of 
tube,  if  the  objective  is  without  collar.  We  cannot  instruct 
in  this  matter.  The  screw  collar  or  the  length  of  tube  is  to  be 
altered  gradually  till  the  hair  under  observation  is  shown  as 
long  as  it  can  be  shown,  as  black  also  and  as  finely  pointed. 
In  critical  image  work  it  is  better  to  choose  one  hair  and  con¬ 
fine  the  attention  to  that  hair ;  if  the  object  be  not  flat,  of 
course  other  hairs  will  not  be  equally  sharp,  but  we  have  noth¬ 
ing  to  do  with  that ;  our  business  is  to  get  a  perfect  image  of 
our  one  object.  If  we  require  the  best  general  photo-micro¬ 
graph  of  our  “  tongue  ”  we  must  set  about  it  by  method  No.  2. 

The  objective  being  corrected,  and  the  image  perfect  as  seen 
with  the  ordinary  eye-piece,  the  latter  is  removed  and  the  pro¬ 
jection  ocular  substituted ;  the  image  is  then  projected  first 
upon  the  ground  glass  of  the  camera.  Assuming  that  a  pro¬ 
jection  ocular  of  the  type  made  by  Zeiss  is  to  be  used,  we  have 
next  to  focus  the  diaphragm  of  this  ocular  upon  our  ground 
glass,  where  a  round  disc  due  to  the  diaphragm  in  the  ocular 
will  be  seen.*  This  is  easily  done  by  observation,  twisting 
round  the  moveable  part  of  the  ocular,  where  we  shall  find  a 
scale  and  an  index  put  there  for  the  purpose.  Next  the  image, 
having  been  carefully  centred  on  the  ground  glass,  is  accurately- 
focused  on  the  plain  glass  prepared  as  suggested  on  page  53. 
Here  again  we  can  not  instruct ;  it  is  a  matter  of  experience 
to  focus  a  difficult  image.  With  objectives,  other  than  apo- 
chromatic,  fringes  of  color  are  usually  found  round  the  critical 
part  of  the  image  ;  very  often,  with  ordinary  objectives,  the 
focus  will  be  found  correct  when  the  colors  seen  are  claret  and 
green ;  but  this  depends  on  the  correction  for  color  given  to 
the  lens  by  the  optician.  The  apocliromatic  lenses,  in  our 

*  If  the  image  of  the  diaphragm  as  projected  is  larger,  we  may  have  to 
slew  the  camera  a  little  in  order  to  see  the  edge  of  the  projected  disc 
image. 


86 


PRACTICAL  PHOTO-MICROGRAPHY. 


experience,  give  little  or  no  color  which  is  not  in  the  object, 
and  we  never,  with  these  lenses,  find  fringes  of  color.  But  we 
>  find  the  focusing  as  easy  with  one  glass  as  the  other ;  it  is  only- 
after  development  that  the  superiority  of  the  apochromatic 
glasses  shows  itself  unmistakably. 

When  we  use  u  Bamsden  ”  or  “  Aplanatic  ”  focusing  ocular 
color  is  often  seen  in  the  objects,  but  we  must  not  attribute  that 
to  the  objective.  If  this  color  is  objected  to,  a  very  low-power 
ocular  made  by  Zeiss,  and  called  a  “  Searcher  Eye-piece,”  may 
be  sunk  in  a  plaque  of  wood,  that  is  to  say,  the  eye-piece  may 
be  thrust  through  a  hole  in  the  wood  to  such  a  distance  that 
when  the  wood  occupies  the  place  of  the  ground  glass  or  sensi¬ 
tive  plate,  the  diaphragm  of  the  eye-piece  occupies  the  critical 
plane  where  the  image  is  to  fall  on  the  sensitive  plate.  Several 
holes  may  be  bored  in  the  plaque  of  wood,  and  the  eye-piece 
may  then  be  moved  from  hole  to  hole. 

Under  the  next  set  of  examples  we  may  put  a  very  large 
series #of  objects — always  overlooking,  for  the  present,  the  pho¬ 
tographic  difficulties  of  color  to  which  an  entire  chapter  is 
allotted — such  objects,  for  instance,  as  the  easier  diatoms ;  phy¬ 
siological,  histological  and  pathological  subjects ;  insect  structure 
and  the  larger  bacteria  where  no  minute  structure  is  to  be 
shown,  as  flagella.  For  all  such  subjects  where  the  magnifica¬ 
tion  required  is  from  forty  diameters  upwards,  the  substage 
condenser  with  bull’s-eye  may  be  used,  and  the  focus  in  such 
cases  should  be  general  rather  than  critical.  Below  forty 
diameters  the  writer  avoids  the  use  of  a  magnifying  glass  for 
focusing,  believing  that  a  better  general  focus  is  obtained  with¬ 
out  the  Bamsden;  he  admits,  however,  that  his  eyesight  is 
possibly  abnormally  sharp.  As  soon  as  the  power  used  is 
sufficiently ^high  to  magnify  the  focused  flame-image  so  as  to 
make  it  cover  the  whole  field  to  be  photographed;  i.  e.,  in  all 
magnifications  over  say  400  diameters,  the  writer  always  dis¬ 
penses  with  the  bull’s-eye.  As  already  pointed  out,  the  size  of 
the  flame-image  on  the  field  depends  in  the  first  place  on  the 
focus  of  the  condenser,  in  the  next  place  upon  the  combined 
power  of  objective  and  ocular.  As  the  writer  progresses  in 
experience  he  uses  the  bull’s-eye  less  and  less  in  his  work.  In 


PRACTICAL  PHOTO-MICROGRAPHY. 


87 


fact  he  has  of  late  discarded  it  almost  entirely.  Perhaps  the 
best  plan  is  to  omit  the  bull’s-eye  and  use  a  condenser  of  such 
focal  length  as  to  project  on  the  object  a  sufficiently  large 
image  of  the  radiant. 

Photo-micrography  of  deep  objects,  as  many  diatoms,  is  a 
vexed  question  which  the  writer  prefers  to  leave  undiscussed. 
The  reader  must  judge  for  himself  whether  he  is  to  get  the 
best  general  appearance  of  his  object,  whether  he  prefers  to 
resolve  one  plane  without  attention  to  any  other  plane,  or 
whether  he  will  be  best  suited  by  a  compromise,  that  is,  by  a 
little  resolution  with  fair  general  sharpness.  One  thing  he 
need  not  attempt,  viz. :  to  get  perfect  resolution  on  several 
planes  simultaneously. 

The  achievements  of  the  most  difficult  photo-micrography 
are  vouchsafed  only  to  the  most  careful  and  skillful  operator. 
There  is  no  secret  in,  nor  any  royal  road  to  the  photography  of 
the  flagellum  of  a  microbe,  or  the  “  dots  ”  on  P.  angulahim. 
Good  optical  appliances,  absolute  freedom  from  tremor, 
efficiency  in  centering,  correcting  and  focusing,  are  the  only 
secrets.  Skill  in  these  matters  can  only  be  acquired  by  long, 
earnest,  unflagging  study  and  practice.  An  occasional  rush 
will  not  do  for  this  work ;  it  is  necessary  to  give  up  to  it  the 
entire  attention  for  the  time  being,  and  there  is  no  use  for  any 
person  to  attempt  this  work  at  any  odd  moment,  for  failure  is 
sure  to  result. 

Above  all  we  would  counsel  our  reader  to  study  the  science 
of  correcting  his  objectives  by  collar  or  tube  ;  centering  and 
focusing  are  mechanical,  and  follow  definite  and  patent  rules ; 
“  correction  ”  is  never  alike  for  two  objects,  and  is  a  matter  of 
sheer  accuracy  of  observation  the  highest  quality  a  micro- 
scopist  can  possess. 

In  a  later  chapter  we  shall  specify  certain  difficult  and  com¬ 
mon  test  objects  giving  hints — and  only  hints — how  the  work 
may  be  attempted. 


CHAPTEK  XIII. 


EXPOSURE. 

There  is  not  a  subject  more  important,  nor  any  more  diffi¬ 
cult  to  deal  with,  than  this  one.  We  shall  make  it  even  more 
important  in  photo-micrography  than  it  is  in  general  photog¬ 
raphy,  because  we  propose  to  advise  the  reader  not  to  alter  to 
any  serious  extent  the  constituents  or  proportions  of  his  devel¬ 
oping  solution.  It  is  a  more  difficult  subject  here  than  even 
in  general  photography,  for  whatever  be  the  colors  of  the  ob¬ 
jects  actually  photographed  in  the  latter  branch,  there  is  al¬ 
ways  a  very  large  amount  of  reflected  white  light  which  to  a 
vast  extent  lessens  the  difficulties  arising  from  the  colors  of 
the  objects  themselves.  Had  we  to  photograph  a  landscape 
entirely  by  transmitted  light,  were  such  a  thing  possible,  the 
result  would  be  curious ;  in  photo-micrography  practically  99 
per  cent,  of  our  light  is  transmitted,  opaque  objects  being 
rarely  photographed. 

We  may  state  at  once  that  we  do  not  approve  of  the  sys¬ 
tem  of  trying  to  give  rules  for  exposure  ;  rules  and  tables 
doubtless  assist  the  beginner  at  first  but  leave  him  helpless  in 
the  end.  Moreover,  it  is  futile  to  attempt  to  give  rules,  for  it 
is  impossible  to  take  into  account  the  most  puzzling  of  all 
photo-micrographic  conditions ,  that  of  color.  If  we  worked 
only  on  colorless  objects,  we  could  easily  give  a  most  useful 
code  of  exposures,  but  no  such  state  of  thing  obtains,  a  color¬ 
less  object  is  very  rare  in  photo -micrography.  We  propose 
rather  to  begin  at  the  other  end,  and  to  inform  our  reader 
how  to  know  after  exposure  where  he  has  erred ;  and  by  this 
means  he  will  not  only  very  soon  arrive  at  the  proper  exposure 
for  the  particular  object  in  hand,  but  he  will  gain  experience 
by  every  exposure  he  makes.  By  far  the  nearest  approach  to 
a  scientific  judgment  of  exposures  that  we  know  is  the  table 


PRACTICAL  PHOTOMICROGRAPHY. 


89 


of  Dr.  E.  C.  Bousfield  already  alluded  to  (p.  14),  as  his 
table  is  copyright  we  do  not,  even  with  his  permission,  pro¬ 
pose  to  use  it  here.  , 

The  factors  on  which  exposure  mainly  depends,  excluding 
from  our  consideration  color,  are 

1.  Illumination. 

2.  Magnification. 

1.  Illumination.  We  can  no  more  lay  down  rules  with  re¬ 
gard  to  this  than  with  regard  to  color.  An  oil  lamp  is  the 
weakest  light  generally  used,  the  lime  light  next,  magnesium 
next,  the  electric  light  next,  sunlight  the  most  powerful. 
But  all  depends  on  how  they  are  used ;  lime  light  properly 
burning  and  properly  used  may  be  much  more  active 
on  our  plate  than  diffused  daylight.  As  we  propose  to  con¬ 
sider  here  artificial  light  only,  and  specially  the  lights  we 
know  best,  oil  and  lime,  we  need  only  say  that  the  lime  light 
may  be  from  10  to  50  times  as  powerful  and  as  actinic  as  the 
best  oil  lamp. 

The  effect  of  the  condenser  properly  used  is  astounding  to 
the  beginner,  the  bull’s-eye  sometimes  increases  and  sometimes 
diminishes  the  force  of  the  light. 

The  beginner  after  producing  a  negative  will  find  it  very 
difficult,  even  with  the  instructions  to  follow  on  later  pages, 
to  form  a  correct  opinion  as  to  whether  his  negative  is  over, 
under,  or  properly  exposed.  His  best  plan  is  probably  to 
show  his  negative  to  some  experienced  photographer  who  will 
be  able  to  give  a  certain  amount  of  help  as  to  the  steps  to  be 
taken  in  future.  But  even  the  experienced  photographer, 
and  in  some  cases  even  the  experienced  photo-micrographer, 
will  be  at  a  loss  to  decide  whether  a  negative  is  over  or  under 
exposed.  In  this  case  the  only  thing  to  be  done  is — if  the 
prints  are  not  satisfactory — to  try  a  longer  exposure  and  a 
shorter  one.  Exposures  should  be  varied  by  geometrical 
rather  than  arithmetical  progression ;  that  is,  if,  for  example, 
an  exposure  of  40  seconds  is  found  to  be  wrong,  it  is  well  to 
try  20  or  80,  or  even  10  or  100  seconds  rather  than  35  or  50. 

A  weak  background  ( i .  e.,  a  ground  grey  in  the  negative  and 
dirty  white  in  the  print)  is  a  sure  sign  of  one  of  three  faults : 


90 


PRACTICAL  PHOTO-MICROGRAPHY. 


1.  Under-exposure;  2.  Reflected  light  inside  the  apparatus ;  3. 
Too  much  light,  or  rather,  too  much  angle  not  necessarily 
over-exposure  (over-exposure,  under  certain  conditions  and  to 
a  certain  degree,  causes  also  grey  backgrounds;  but  in  this 
case,  as  we  shall  see  later,  the  whole  image  is  grey). 

If  we  are  dealing  with  a  colored  object  we  are  practically 
compelled  to  disregard  all  circumstances  except  that  of  color. 
Color  upsets  every  calculation  of  exposures  that  human  ingen¬ 
uity  can  devise.  Reds  and  yellows  sometimes  cause  us  to  in¬ 
crease  our  exposure  a  hundred  fold,  but  there  are  reds  which, 
being  bluish  (as  eosin,  a  favorite  stain  with  many  for  certain  ob¬ 
jects),  upset  all  our  previous  calculations.  Violets  are,  of  course, 
as  a  rule,  highly  actinic,  aud  require  very  brief  exposures,  but 
logwood,  as  an  example,  stains  certain  tissues  to  a  violet  so  full 
of  red  that  again  we  may  be  completely  at  sea  in  our  exposure. 
The  writer  has  daily  experience  of  such  puzzling  conditions. 
Yellows,  in  like  manner,  are  in  certain  objects  practically 
almost  chemical  opacity,  while  in  other  cases  their  contrast 
with  the  white  ground  is  so  small  as  to  render  great  the  diffi¬ 
culty  of  differentiating  between  the  yellow  and  pure  white. 
A  red,  a  violet,  and  a  yellow  may  each  be  either  very  easy  or  al¬ 
most  impossible  to  render  by  ordinary  photography ;  a  mixture, 
such  as  a  double  stain  of  violet  and  red,  is  very  often,  with¬ 
out  “  color  correct  ”  or  “  orthochromatic  ”  photography,  a  com¬ 
plete  impossibility. 

In  view  of  conditions  so  common,  yet  so  puzzling,  we  again 
submit  that  any  table  of,  or  rule  for,  exposure  would  be  out  of 
the  question  :  what  we  may  do,  and  propose  to  try  to  do,  is  to 
give  guides  by  which  the  reader,  on  developing  his  negative, 
whatever  the  subject  may  have  been,  may  be  able  to  correct 
at  next  trial  any  error  he  may  have  made  in  his  first  exposure. 

Appended  to  each  of  the  illustrations  of  this  book  we  have 
noted  the  exposure  given  by  us  in  producing  the  negative,  but 
even  this  attention  on  our  part  is  only  of  minor  value  on 
account  of  our  inability  to  gauge  the  quantity  and  quality  of 
of  the  light  actually  reaching  our  sensitive  plate. 


CHAPTER  XIV. 


DEVELOPMENT  OF  GELATINE-BROMIDE  PLATES. 


Normal  Developers. 
A . — Pyro-Ammonia. 


Pyrogallol .  2  grains 

Liq.  Amm.  .880 .  3  minims 

Potassic  or  ammonic  bromide .  1  grain 

Water  to .  1  ounce 


B. — Pyro-Carbonate. 


1.  — Pyrogallol .  3  grains 

Sodic  carbonate . 12  grains 

Water  to .  1  ounce 

Or, 

2.  — Pyrogallol .  3  grains 

Potassic  carbonate . 12  grains 

Water  to .  1  ounce 

Or, 

3.  — Pyrogallol .  3  grains 

Sodic  carbonate .  6  grains 

Potassic  carbonate . 6  grains 

Water  to .  1  ounce 


Notes. — The  reader  is  referred  to  Chapter  VIII  for  hints  as 
to  method  of  “  stocking  ”  the  above  reagents.  The  stock  solu¬ 
tions  there  formulated  are  all  so-called  “  10  per  cent,  solutions,” 
and  in  each  case  a  grain  or  a  minim  may  be  obtained  by  tak¬ 
ing  ten  minims  of  the  stock  solution. 

Thus  to  make  the  Normal  Pyro-Ammonia  Developer  we 


take  of 

Stock  pyro  solution . 20  minims 

Stock  Ammonia . 30  minims 

Stock  Bromide . 10  minims 


and  make  up  with  water  to  one  ounce. 


92 


PRACTICAL  PHOTO-MICROGRAPHY. 


To  make  the  Normal  Pyro-Carbonate  Developer  No.  3  : 


Stock  Pyro  Solution . 30  minims 

Sodic  and  Potassic  Carbonate  Solution . 120  minims 

(=2  drams). 

Bromide . . . None. 


Make  up  with  water  to  one  ounce.  (No  account  is  taken  of 
the  chemicals  used  merely  to  preserve  the  pyro.) 

Normal  Developer  G.  Ferrous  Oxalate. 

Take  of  the  saturated  solution  of 


Potasssic  oxalate .  4  parts 

Ferrous  sulphate .  1  part 


Be  careful  to  pour  the  Ferrous  Sulphate  Solution  into  the  Pot¬ 
assic  Oxalate  and  not  vice  versa. 

(Note. — The  writer  does  not  recommend  the  Ferrous  Oxalate 
Developer  for  ordinary  photo-micrographic  work.  This  is  not 
denying  that  it  is  excellent  in  some  hands  and  for  some  kinds  of 
subject.  The  reader  is  advised  to  try  the  effect  for  himself ; 
as  a  general  developer  it  has  some  recommendations.) 

The  plate  after  exposure  is,  in  non-actinic  light,  (see  pp.  55 
and  56,)  placed  film  upwards  in  a  black  developing  tray,  and 
the  developing  solution  is  deftly  swept  over  it ;  the  developer 
must  not  be  poured  upon  one  spot  but  “  swished  ”  with  a  side 
motion  all  over  the  plate,  so  that  as  far  as  possible  the  plate 
may  be  all  wetted  at  once.  Some  workers  prefer  to  soak  the 
plate,  till  the  gelatine  is  all  wet,  in  plain  water  before  applying 
the  developer ;  this  procedure  does  no  harm  if  air  bubbles  that 
may  form  are  removed  with  a  clean  brush  or  finger.  In  all 
cases  the  inexpert  must  be  prepared  for  air  bubbles  and  remove 
them  if  they  occur. 

In  a  certain  number  of  seconds  the  image  ought  to  begin  to 
appear.  The  first  thing  that  regulates  the  time  required  for 
this  first  appearance  is  the  quality  or  treatment  of  the  gelatine 
used  in  the  emulsion ;  this  factor  need  not  be  taken  into  much 
account.  But  the  important  matter  is  to  observe  the  quality 
of  the  image  at  the  time  of  its  first  appearance,  and  still  more 
is  it  important  to  note  most  carefully  the  pace  at  which  the 
details  follow  each  other.  As  a  rule  an  overexposed  plate 
will  show  some  of  the  details  before  an  underexposed 


PRACTICAL  PHOTO-MICROGRAPHY. 


93 


plate  of  the  same  batch  would  do  so.  If  with  any  of  our 
“Normal  Developers”  no  image  at  all  is  visible  after 
thirty  seconds,  the  plate  may  be  put  down  as  underex¬ 
posed.  The  image  appears  in  the  following  order  of  rapidity 
with  our  three  Normal  Developers  :  1st  Pyro- Ammonia ;  2nd 
Pyro-Carbonate ;  3d  Ferrous  Oxalate.  This  is  to  be  taken  as 
a  general  rule  in  comparing  the  Carbonate  with  the  Oxalate 
developer.  Bromide  always  slows  the  appearance,  and  also 
the  acquisition  of  density  and  detail,  of  the  image  and  free 
bromide  in  the  developer  has  a  much  greater  apparent  effect 
on  the  carbonate  and  ferrous  developers  than  on  the  ammonia 
developer.  Half  a  grain  of  bromide  in  the  carbonate  or  fer¬ 
rous  developer  has  at  least  as  much  retarding  effect  as  a  grain 
in  the  ammonia  developer.  Bromide  restrains  both  detail  and 
density,  but  luckily  it  restrains  detail  more  than  density.  The 
chief  use  of  free  bromide  in  the  developer  is  to  give  us  time 
to  watch  progress  and  to  stop  progress  at  the  proper  moment, 
but  bromide  is  absolutely  necessary  to  prevent  fog  with  certain 
plates  used  with  the  ammonia  developer.  In  the  case  of  the 
carbonates  the  carbonic  acid  evolved  acts  as  a  restrainer  and 
retarder ;  in  the  case  of  the  ferrous  oxalate,  ferric  bromide  is 
formed  in  considerable  quantity,  and  restrains  and  retards  de¬ 
velopment.  Hence  a  ferrous  oxalate  developer  used  over  and 
over  again  works  each  time  more  slowly  and  more  feebly  than 
the  time  before.  We  deprecate  the  repeated  use  of  the  same 
dose  of  pyro-developer ;  but  repeated  use  of  one  dose  of  ferrous 
oxalate  is  quite  permissible  up  to  a  point  which  will  easily  be 
known  by  muddiness  of  the  solution,  and  slowness  of  its  action. 

If  the  image  starts  about  10  or  15  seconds  after  the  devel¬ 
oper  is  applied  to  the  plate,  we  must  be  prepared  for  over¬ 
exposure  of  the  high  lights  at  least.  With  subjects  presenting 
violent  contrasts  of  density  or  color-actinism,  we  are  almost 
bound  to  over-expose  the  high  lights ;  but  with  ordinary  sub¬ 
jects  the  image,  if  it  appears  at  all  in  15  seconds,  should  show 
only  the  highest  lights  at  that  stage  ;  and  the  half  tones  of  a 
properly  exposed  plate  will  follow  the  high  lights  without 
any  lagging  or  apparent  reluctance.  In  fact,  the  develop¬ 
ment  should  proceed  steadily,  without  stoppage  and  without 
precipitancy  from  start  to  finish,  so  far  as  detail  is  concerned. 


94 


PRACTICAL  PHOTO-MICROGRAPHY. 


The  details  that  first  appear  under  any  of  our  normal  devel¬ 
opers  must  be  most  carefully  scrutinized,  because  upon  their 
appearance  we  shall  to  a  great  extent  base  our  judgment  of 
exposure.  If  the  first  details  are  pale  gray  and  are  hurriedly 
followed  by  others  almost  equally  gray  the  plate  is  over-ex¬ 
posed  ;  if  the  first  details  rapidly  become  black,  while  other 
details  are  either  pale  gray  or  invisible,  the  plate  is  certainly 
under-exposed.  If  the  whole  plate  become  very  quickly  gray 
over-exposure  is  certain ;  if  the  whole  plate  become  dense 
black,  or  dense  black  and  dark  gray,  a  less  degree  of  over-ex¬ 
posure  is  the  probable  cause. 

Experience,  and  a  certain  amount  of  allowance  for  the 
nature  of  the  subject,  are  both  necessary  in  judging  of  ex¬ 
posure  by  observation  of  the  appearances  during  development ; 
but  when  experience  has  been  gained,  and  a  variety  of  sub¬ 
jects  photographed,  the  worker  will  be  able  very  accurately 
to  judge  where  and  how  much  he  has  erred — if  he  has  erred 
— in  exposure.  But  two  things  are  settled :  An  image 
homogeneous  in  color  all  over  is  an  over-exposed  image ;  an 
image  which  is  white  in  any  part  when  development  is  com¬ 
plete  is  an  under-exposed  image,  unless  we  have  a  subject 
requiring  absolute  blackness  in  our  print,  such,  for  instance,  as 
a  “dark-ground”  subject.  If  some  part  of  our  object  be 
nearly  opaque  or  highly  non-actinic  in  color,  as  many  patho¬ 
logical  and  physiological  red  stains,  we  have  but  two  courses 
open  to  us.  1st.  To  deliberately  over-expose  the  high  lights 
or  actinic  colors  to  such  an  extent  as  will  allow  development 
of  the  opaque  or  non-actinic  parts.  Y ery  often  this  method  is 
unexpectedly  successful,  the  high  lights  not  being  so  much 
overexposed  as  might  have  been  feared ;  or  2nd.  We  must  use 
a  color  correct  plate,  cutting  off,  if  necessary,  the  over-actinic 
rays  by  suitable  screens.  (See  chapter  XYI.) 

Another  matter  resting  chiefly  on  experience,  and  almost 
impossible  to  treat  usefully  in  a  book,  is  the  amount  of  devel¬ 
opment  required.  In  most  cases  when  details  are  all  “  up,” 
not  necessarily  distinguishable  but  at  least  developed,  the 
density  of  the  negative  after  fixation  would  not  be  sufficient 
to  yield  good  prints  by  any  of  our  usual  processes.  Now  in 


PRACTICAL  PHOTOMICROGRAPHY, 


95 


the  course  of  development  as  a  rule  sufficient  bromide  is 
evolved  (beyond  the  soluble  free  bromide  we  put  into  the  de¬ 
veloper),  to  greatly  retard  if  not  to  arrest  the  growth  of  detail 
and  density.  Where  the  subject  itself  presents  violent  contrasts 
it  is  well  to  expose  to  such  an  extent  that  the  first  dose  of 
developer  shall  reveal  all  detail  without  undue  density  in  any 
part.  Where  the  high  lights  or  actinic  colors  are,  as  above 
advised,  deliberately  over-exposed  in  such  subjects,  the  action 
known  to  photographers  as  the  “reversing  action  of  light” 
comes  in,  and  these  over-exposed  high  lights  in  place  of  being 
densely  black  in  the  negatives,  undergo  the  reversing  action 
and  refuse  to  develop  density.  This,  of  course,  suits  us  ad¬ 
mirably  in  the  cases  under  consideration — of  violent  contrasts. 
But  if  the  subject  be  an  ordinary  one  without  violent  contrasts, 
or  if  we  require  as  nearly  as  possible  a  black  and  white  render¬ 
ing  of  such  objects  as  diatoms,  then  we  find  that  when  detail 
is  all  “  up  ”  density  is  insufficient,  and  we  reinforce  our  de¬ 
veloper  with  alkali.  In  the  case  of  the  carbonates,  time  will 
produce  the  desired  effect,  because  though  retarders  are  being 
evolved  there  is  no  volatilization  of  the  alkali ;  but  with  am¬ 
monia  as  the  alkali,  not  only  is  fresh  bromide  being  evolved- 
but  the  original  alkali  is  evaporating,  so  we  generally  add 
about  1^  minim  of  ammonia  (15  minims  of  our  10  per  cent.) 
to  each  ounce  of  developer  as  soon  as  there  appears  to  be  a 
halting  in  the  acquisition  of  detail  or  density. 

To  know  when  to  stop  development  is  a  very  serious  matter. 
Many  so-called  rules  have  been  laid  down,  and  many  hints 
given  on  the  point,  but  we  have  never  found  any  such  rule  or 
hint  to  cover  many  cases.  The  image  is  not  fully  developed 
as  a  rule  until  some  part  of  it  is  visible  from  the  back  of  the 
plate,  any  further  examination  of  the  back  may  inform  us  of 
the  nature  of  the  gelatine,  of  the  nature  of  our  subject,  of  the 
degree  to  which  the  emulsion  has  been  “cooked,”  but  that  is 
all.  If  we  have  a  standard  non-actinic  light,  through  the  col¬ 
ored  medium  guarding  which  we  can  see  the  flame  through 
the  plate,  we  shall  by  experience  come  to  judge  very  fairly 
whether  a  plate  of  a  batch  we  know  is  sufficiently  developed. 
The  flame  should  be  barely  discernable  as  to  shape  through 


96 


PRACTICAL  PHOTO-MICROGRAPHY. 


the  dark  parts  of  the  negative ;  the  whole  plate  should  look  as 
if  it  would  be  a  very  great  deal  too  dark  but  for  the  fixing 
operation,  But  it  must  by  no  means  be  opaque  nor  equally 
dark  all  over,  nor  must  there  be  any  part  where  the  shape  of 
the  flame  is  clearly  visible,  as  through  clear  glass.  Looking  at 
the  face  (film)  of  the  plate,  some  parts  should  seem  quite 
black,  others  dark-gray,  others  (the  shadows)  paler  gray  but 
not  white.  Practice  alone,  and  as  before  consideration  of  the 
various  qualities  of  various  subjects,  can  ever  teach  us  what  is 
perhaps  our  most  difficult  lesson  next  to  proper  exposure,  viz. : 
when  to  stop  development. 

In  cases  of  error  in  exposure,  if  the  error  is  but  slight  we 
can  almost  always  make  our  negative  as  good  as  if  we  had  ex¬ 
posed  correctly.  And  further,  there  are  certain  subjects  which 
cannot  by  exposure  alone  without  a  little  “  dodging  ”  in  after 
processes  be  rendered  to  the  best  advantage.  We  have  sug¬ 
gested  a  method  of  treatment  for  subjects  presenting  violent 
contrasts.  We  presently  shall  touch  on  other  abnormal  sub¬ 
jects. 

But  we  must  now  mention  another  system  of  development 
•which  has  marked  advantages  for  the  beginner ;  its  chief  dis¬ 
advantage  being  that  in  using  it  we  have  not  the  same  useful 
guides  to  judgment  of  exposure.  This  system  is  usually  called 
slow  development,  and  as  a  rule  the  carbonates  are  the  alkalis 
used.  The  difference  consists  simply  in  starting  development 
with  a  very  weak  developing  solution,  and  adding  the  reagents 
if  necessary  little  by  little  till  the  full  normal  dose  is  reached 
or  the  full  effect  produced.  Thus  we  may  start  with  pyro,  2 
grains ;  bromide,  1  grain ;  ammonia,  1  minim ;  and,  after 
(say)  3  minutes  add  a  minim  more  of  ammonia,  and  so  on  for 
a  space  of  from  20  minutes  upwards,  or  we  may  start  with 
only  5  or  6  grains  of  the  combined  carbonates  and  pursue  a 
similar  course.  The  writer  has  never  in  ordinary  photography 
found  the  slightest  benefit  to  arise  from  such  a  prolongation 
of  development,  unless  it  be  that  in  certain  cases  more  contrast 
of  light  and  shade  is  obtained  by  the  slow  method.  The  tyro 
has  perhaps  more  time  to  make  up  his  mind  when  to  stop  de¬ 
velopment,  but  in  the  system  recommended  by  us  he  has  cer- 


PRACTICAL  PHOTO-MICROGRAPHY. 


97 


tainly  3  minutes,  probably  4  or  5,  to  examine  progress,  and  he 
can  hardly  want  more ;  further,  by  the  slow  process  15  or  20 
minutes  will  be  needed  simply  perhaps  to  find  out  that  another 
exposure  is  required.  Those,  however,  who  lean  towards  slow 
development  may  refer  to  any  of  the  Scovill  series  of  photog¬ 
raphic  books,  where  they  will  find  full  details. 

Abnormal  Development. 

It  has  been  said  that  if  the  error  in  exposure  has  been  but 
trifling  a  perfect  negative  may  still  be  made.  It  is  better  in 
most  cases  to  make  a  fresh  exposure,  but  this  proceeding  may 
not  at  all  times  suit  the  worker,  and  further  it  is  well  to  gain 
a  little  mastery  over,  and  tact  in,  manipulation  of  the  developer. 

If  appearances  cited  above  show  that  the  plate  has  certainly 
been  underexposed,  the  developer  should  at  once  be  thrown 
away  and  the  plate  washed.  Thereafter  a  fresh  developer  is 
applied  containing  less  pyro  and  bromide.  Thus  :  Pyro  1  to 
grains.  Bromide  a  grain.  Ammonia  as  before.  Or 
water  may  be  added  to  the  first  developer  which  is  to  be  im¬ 
mediately  reinforced  with  alkali.  If  the  plate  is  known  before 
development  to  be  underexposed  to  a  considerable  extent,  it 
may  be  soaked  in  the  alkali  and  water  of  the  developer  alone 
for  a  couple  of  minutes,  the  pyro  and  a  modified  quantity  of 
bromide  to  be  added  thereafter.  But  an  underexposed  plate 
as  a  rule  is  useless,  no  matter  what  we  do  with  it. 

With  overexposure  the  matter  is  different,  for  a  plate  grossly 
overexposed  can  be  saved  if  it  is  taken  in  time.  The  difficulty 
is  to  catch  it  in  time  and  to  apply  the  cure  in  time.  Bromide 
certainly  restrains  detail  but  unfortunately  it  also  keeps  back 
density,  and  in  a  severely  overexposed  plate  density  of  the  high 
lights  is  the  very  thing  most  lacking.  If  the  overexposure  be 
only  enough  to  make  the  plate  very  black  all  over,  or  as  is  the 
usual  case,  very  black  and  dark  grey,  the  simplest  cure  is  to 
add  water  to  the  developer  and  to  stop  development  earlier 
than  if  the  plate  were  properly  exposed.  But  if  the  overex¬ 
posure  has  been  sufficient  to  make  the  image  grey  all  over,  the 
best  plan  is  to  watch  carefully  till  every  detail  seems  out  and 
then  instantly  to  flood  the  plate  with  water  containing,  for 


98 


PRACTICAL  PHOTOMICROGRAPHY. 


every  three  grains  or  one  minim  of  alkali  in  the  developer, 
from  two  to  four  grains  of  sodic  or  potassic,  or  sodic  and  potassic, 
citrate.  (See  page  62.)  This  immediately  stops  all  further 
development  of  detail,  but  does  not  seem  to  affect  density  which 
is  gained  as  follows :  Add  to  the  original  developer,  or  to  a 
freshly  made  one,  two  to  four  grains  of  citrate  for  each  minim 
of  ammonia  or  for  every  three  grains  of  carbonate,  pour  away 
the  water  and  citrate  on  the  plate  and  apply  the  modified  de¬ 
veloper  for  a  minute  or  two.  Then  add  to  the  developer  a 
brisk  dose  of  alkali,  say  two  minims  of  ammonia,  and  continue 
development  till  sufficient  density  is  attained. 

The  carbonates  may  be  restrained  so  easily  and  so  forcibly  with 
bromide,  that  perhaps  the  simplest  way  when  developing  with 
them  is  to  add  (say)  one  grain  of  bromide  for  each  ounce  of 
developer.  Water  alone  added  to  the  carbonate  developer 
sometimes  suffices  to  overcome  moderate  overexposure. 

When  the  subject  dealt  with  is  by  nature  wanting  in  con¬ 
trast  it  will  be  found  useful  to  develop  with  an  ordinary  de¬ 
veloper  until  all  detail  is  up,  and  then  to  add  citrate  to  the  de¬ 
veloper  finishing  as  above  with  the  brisk  dose  of  ammonia. 

The  citrate  was  suggested  by  Mr.  Watmouth  Webster,  now 
of  Chester,  Eng.,  and  from  its  action  in  stopping  detail  but 
not  density  in  development  will  be  found  very  useful. 

We  have  in  this  chapter  formulated  for  one  ounce  of  devel¬ 
oper  only ;  this  quantity  will  develop  a  quarter-plate ;  two 
ounces  a  half -plate  or  7x5,  four  ounces  a  10x8  plate  ;  but  the 
the  beginner  is  advised  to  double  these  quantities  till  he  has 
become  adept  in  evenly  and  quickly  flooding  his  plate. 

During  development  the  plate  should  be  constantly  shielded 
from  light  even  of  the  non-actinic  lamp,  being  uncovered 
only  at  the  time  and  for  the  purpose  of  scrutiny. 

It  may  be  well  to  recapitulate  certain  points  of  this  chapter 
referring  to  certain  appearances  shown  by  a  plate  soon  after 
the  image  has  started  to  appear  in  the  developer,  normal  as 
on  pages  91  and  92. 

Refusal  to  appear  for  one  minute,  or  appearance  in  highest 
fights  only,  bespeaks  utter  underexposure. 

High  fights  grey,  shadows  wanting — severe  underexposure. 


PRACTICAL  PHOTO-MICROGRAPHY.  99 

High  lights  dense  black,  shadows  dirty  grey — under¬ 
exposure. 

High  lights  appear  after  fifteen  to  thirty  seconds,  grey  at 
first,  gradually  darkening,  shadows  creeping  up  steadily  all 
the  time;  finally  high  lights  black  and  shadows  ranging 
from  pale  to  dark  grey — correct. 

High  lights  rapidly  followed  by  shadows,  the  whole  rapidly 
gaining  great  blackness  and  density — overexposure. 

High  fights  and  shadows  appearing  almost  immediately  and 
simultaneously,  the  whole  turning  rapidly  gray  and  remaining 
so — great  overexposure. 

Instant  flashing  out  of  the  whole  image,  all  remaining  a 
very  pale  smokey  grey — enormous  overexposure. 

The  Hydroquinone  Developer.* 

This  system  of  development  has  of  late  been  greatly 
elaborated  and  improved,  especially  since  it  was  found 
feasible  to  use  hydroquinone  in  conjunction  with  the  hydrate 
or  caustic  alkalis  without  damage  to  the  film.  Whether  or 
not  this  is  destined  to  be  the  standard  developer  of  the  future, 
we  are  confident  in  stating  that  it  is  a  very  fine  developer  at 
present.  Indeed,  on  account  of  the  ease  with  which  almost 
any  amount  of  density  may  be  obtained  without  injury  to  the 
shadows,  it  is  probably  the  best  developer  for  photo-micro¬ 
graphic  negatives.  A  further  advantage  is  that  this  developer 
can  be  used  without  the  presence  of  soluble  bromides.  We 
give  a  formula  due  to  Messrs.  Thomas  &  Co.,  of  London; 
though  containing  a  heavy  dose  of  hydroquinone,  it  is  not 
really  expensive,  as  one  dose  of  the  developing  solution  may 
be  used  for  three,  four  or  even  more  plates.  The  formula 


stands  thus : 

a.  Sodic  sulphite .  1  ounce 

Citric  acid . 30  grains 

Aram.  Bromide . 10  grains 

Water  to . 10  ounces 

Dissolve  and  add  hydroquinone . 80  grains 


*  It  is  to  be  hoped  that  hydroquinone  will  soon  be  universally  called 
by  its  shorter  and  systematic  name  :  “  Quinol.” 


100 


PRACTICAL  PHOTOMICROGRAPHY. 


b.  Sodic  hydrate  “  caustic  soda  ” . 80  grains 

Water  (that  has  been  boiled) . .  .10  ounces 


The  developer  consists  of  equal  parts  of  a  and  d. 

The  action  of  this  developer  is  on  the  whole  more  gradual 
than  that  of  a  pyro-ammonia  developer ;  the  density  varies 
chiefly  as  the  exposure,  and  the  shadows  have  a  tendency  to 
develop  more  slowly  and  with  greater  clearness  than  when 
pyro  is  used. 

The  carbonates  may  also  be  used  with  hydroquinone,  but 
such  a  developer  is  much  less  energetic  than  the  above. 

The  writer  frequently  uses  potassic  meta-bisulphite  in  place 
of  the  citric  acid  and  in  less  quantity. 

Potassic  hydrate  is  as  good  as  sodic,  or  better.  It  is  well  for 
the  beginner  to  use  the  above  solution  somewhat  diluted,  say 
with  an  equal  measure  of  water. 


m 


CHAPTER  XV. 


OPERATIONS  FOLLOWING  DEVELOPMENT. 

Fixing,  Clearing,  Intensification,  Reduction. 

After  development  is  judged  to  be  complete  tbe  plate  is  to 
be  carefully  washed  by  non-actinic  light  under  a  tap  for  a 
couple  of  minutes  or  in  a  few  changes  of  water.  It  may  then 
be  placed  in  a  saturated  solution  of  common  alum  ;  but  except 
in  cases  where  plates  have  a  tendency  to  frill,  this  is  not  neces¬ 
sary.  The  plate  is  then  “  fixed  ”  in  a  solution  of  sodic  hypo¬ 
sulphite  made  alkaline.  (See  page  63.)  The  plate  is  to 
remain  in  the  “  hypo  ”  solution  not  only  till  the  white  (un¬ 
altered  argentic  bromide)  has  disappeared  from  the  back,  but 
a  considerable  time  longer.  If  the  plate  is  removed  as  soon  as 
the  white  has  gone,  it  will  deteriorate  to  a  certainty  after  a 
time.  After  fixation,  the  plate  must  be  very  thoroughly 
washed,  preferably  under  a  rose  tap,  for  10  minutes,  or  in  one 
of  the  washing-machines  sold  for  the  purpose.  Several  hours 
are  necessary  in  the  latter  case.  After  the  hypo  is  undoubt¬ 
edly  removed  the  plate  maybe  “cleared”  in  the  acid  alum 
solution  formulated  on  page  63.  In  this  it  may  remain  for 
about  5  minutes  or  longer.  It  is  thereafter  to  be  thoroughly 
washed,  and  racked  to  dry.  The  beginner  at  all  events  is 
recommended  to  make  a  print  from  his  negative  before  he 
ventures  upon  any  other  step  he  may  think  advisable.  The 
negative  should  be  shown  to  an  expert  photographer,  who  will 
instantly  say  if  there  has  been  any  serious  error  of  treatment. 

If  the  negative  is  “thin  ”  or  pale  all  over  and  wanting  in 
contrast,  yielding  on  albumenized  paper  a  “  washed-out”  look¬ 
ing  print,  all  gray  and  no  black,  intensification  may  be  tried. 


102 


PRACTICAL  PHOTO-MICROGRAPHY. 


%  To  Intensify. 

The  negative  being  above  suspicion  of  hypo  is  soaked  in  a 
flat  dish  in  the  solution  of  mercuric  bichloride  and  acid  given 
on  page  63.  When  the  film  is  as  pale  gray  as  it  will  be¬ 
come,  it  is  well  washed  and  placed  in  the  solution  5,  given  on 
the  same  page.  Here  it  will  very  quickly  turn  black  or 
brown;  but  it  must  be  left  in  the  sodic  sulphite  till  it  is  dark 
when  seen  from  the  back  as  well  as  from  the  front.  It  is  then 
washed,  and  will  be  found  to  have  gained  greatly  in  density 
and  printing  quality. 

There  are  many  other  methods  of  intensifying  for  which  we 
refer  the  reader  to  the  photographic  literature  of  the  day.  We 
have  given  the  one  we  prefer  to  all  others,  especially  for  photo¬ 
micrography.  As  a  rule,  however,  intensification  is  to  be 
avoided,  for  it  is  not  only  ticklish  to  perform  but  doubtful — 
under  conditions  not  precisely  established — as  to  its  perman¬ 
ence. 

If  the  finished  negative  is  too  dense,  especially  if  the  shad¬ 
ows  are  clogged,  we  may  have  recourse  to  “  reduction,”  which 
does  not  present  the  same  difficulties  as  intensification. 

Reduction. 

To  Mr.  Howard  Farmer  we  are  indebted  for  a  very  simple 
and  effective  system  of  reducing.  (See  page  63.) 

Soak  the  plate,  carefully  freed  from  acid  after  the  acid  alum 
bath,  in  solution  B,  for  3  minutes.  Put  into  a  cup  a  few  drops 
of  the  solution  A,  and  pour  the  hypo-solution  into  the  same 
cup,  then  returning  the  mixture  to  the  dish  holding  the  plate. 
Reduction  will  at  once  begin  and  its  progress  must  be  watched. 
If  the  action  cease  before  sufficient  effect  is  produced  add  more 
of  A.  When  finished  wash  well  and  drv.  The  Reducer  No. 

V 

2,  given  on  page  63,  may  be  used.  The  plate  is  soaked  in 
A  till  a  gray  film  more  or  less  marked  seems  to  cover  the  im¬ 
age  ;  the  plate  is  then  washed  and  placed  in  solution  B. 

Varnishing. 

If  a  large  number  of  prints  are  likely  to  be  wanted  from  a 
negative  it  is  well  to  varnish  with  a  spirituous  solution  of  shel- 


PRACTICAL  PHOTO-MICROGEAPHY. 


103 


lac,  or  better  with  one  of  the  good  negative  varnishes  sold  for 
the  purpose.  The  instructions  as  to  heating  the  plate  are  to 
be  carefully  followed.  Plain  collodion  makes  a  very  good  and 
usually  sufficient  protection  for  the  film.  What  we  have  to 
avoid  is  damp,  and  of  course  our  negatives  must  not  be 
scratched.  The  only  objection  to  varnish  is  that  if  appreciably 
thick  it  may  prevent  absolute  contact  for  contact  printing, 
perfect  “  sharpness  ”  being  important  in  photo-micrography. 

A  good  negative  presents  gradations  from  nearly  opaque 
highest  lights,  to  clear  but  well  marked  shadow  detail.  The 
shape  of  a  candle  flame  should  be  discernible  with  difficulty 
through  the  very  densest  parts  of  the  negative.  There  should 
be  no  clear  glass ,  but  some  detail  everywhere.  The  higher 
lights  as  well  as  the  deeper  shadows  should  show  detail.  These 
remarks  hold  good  for  nearly  all  kinds  of  subject,  but  there 
are  exceptions. 

If  in  a  negative  we  find  dense  lights  in  close  juxtaposition 
with  clear  shadows  the  negative  is  underexposed,  unless  the 
subject  is  for  u  black  and  white  ”  rendering. 

If  any  part  is  absolutely  opaque  and  (1)  some  parts  are  quite 
clear,  underexposure,  or  (2)  all  other  parts  too  dense,  overex¬ 
posure,  is  the  probable  cause.  If  the  negative  is  grey  all  over, 
nothing  in  it  approaching  opacity — overexposure,  or  under¬ 
development. 

If  the  negative  is  clear  nearly  all  over,  underexposure  is 
certain  to  be  the  fault. 

Frilling  and  blistering  are  not  often  met  with  now-a-days. 
If  a  plate  frills  before  it  goes  into  the  fixing  solution  it  is  a  bad 
look  out  for  that  batch ;  frequently  the  carbonates  if  long 
applied  in  the  developer  cause  frilling  or  isolation  of  the  whole 
film ;  ammonia  has  not  this  tendency.  If  the  blistering  or 
frilling  appear  on  first  washing  after  the  hypo,  a  cure  will 
usually  be  found  in  soaking  the  plates  straight  from  the  hypo 
in  a  tray  of  common  salt  and  water,  say  one  part  to  twenty. 
Too  strong  hypo  solution  may  cause  blisters. 

Fog,  which  is  easily  recognized  when  seen,  must  be  traced 
to  its  source.  If  the  parts  of  the  plate  protected  during  ex¬ 
posure,  as  by  the  paper  mask,  or  by  the  rebates  or  corners  of 


104 


PRACTICAL  PHOTO-MICROGRAPHY. 

the  dark  slide,  are  degraded  and  fogged,  either  the  plates  are 
foggy  by  nature  or  the  light  of  the  operating  room  is  unsafe. 
If  the  protected  parts  of  the  plate  are  quite  clear,  we  must  look 
to  overexposure,  or  failing  that  to  reflections  inside  the  camera. 
Black  streaks  across  a  negative  mean  stray  light  reaching  the 
plate,  and  the  sharper  are  the  outlines  of  the  streak  the  nearer 
to  our  plate  must  we  look  for  the  leakage.  A  hole  in  the  dark 
slide  makes  a  much  sharper  streak  than  one  of  the  same  size  in 
the  camera  front. 

Uneven  lighting  is  a  very  frequent  cause  of  failure,  but  its 
results  on  the  negative  are  not  difficult  to  recognize,  except  as 
in  next  paragraph. 

There  are  many  defects  to  which  plates  are  liable,  but  we 
cannot  enter  into  details  of  such  things  here.  Uneven  coating 
has  often  the  semblance  of  uneven  lighting  ;  careless  packing 
often  produces  details  on  our  negatives  not  projected  by  our 
objectives. 

Transparent  spots  of  minute  size,  called  “Pinholes”  are 
caused  by  dust  adhering  to  the  film,  these  spots  have  as  a  rule 
no  nucleus ;  but  dust  in  the  emulsion  usually  produces  spots 
that  have  nuclei.  Each  plate  must  be  dusted  with  a  clean 
camel  hair  brush  before  being  put  into  the  slide. 


No.  2. — Typhoid  Bacilli  in  Intestine,  X  750. 


Plate  III. 


CHAPTER  XYI. 


COLOR-CORRECT  PHOTOGRAPHY. 

“  Ortho-Chromatic,”  or  as  we  prefer  to  call  it,  “  Color- 
Correct  ”  Photography,  is  one  of  the  latest  important  improve¬ 
ments  in  our  science.  It  may  be  well  to  explain  the  rationale 
of  this  modification  of  common  processes,  and  the  reader  is 
begged  to  study  carefully  our  introductory  remarks  to  this 
chapter. 

It  has  been  probably  remarked  by  all  observant  people  that 
while  the  colors  yellow,  bright  red,  and  certain  greens  appear 
to  the  eye  the  most  luminous  colors,  they  are  in  photography 
rendered  as  dark,  or  at  least  as  below  the  average  grade  of 
light,  in  the  landscape,  portrait,  or  copy  of  a  colored  drawing. 
On  the  other  hand  the  indigo  and  violet  colors  of  an  object 
seen  in  the  usual  way  appear  to  the  eye  dark  or  at  least  sub¬ 
dued  tints ;  while  these  colors,  when  portrayed  in  the  mono¬ 
chrome  of  photography,  are  represented  as  high  lights.  This 
has  always  been  a  serious  objection  to  photographic  ren¬ 
dering  of  many  objects,  notably  of  painted  pictures,  and  to  a 
considerable  extent  of  landscape  with  foliage  and  sky  effects. 
It  is  evidently  a  very  serious  objection  to  photo-micrography 
if  we  render  an  object,  stained  (say)  with  the  dark  violet  of 
logwood  and  the  bright  red  of  eosine  or  magenta,  the  very 
opposite  of  what  it  really  is  visually ;  viz. :  bright  in  the  print 
where  the  object  is  dark  violet,  and  dark  in  the  print  where  in 
the  section  there  is  a  fine  glittering  red.  Further,  if  we  have 
an  object  entirely  red  or  entirely  yellow  but  in  gradations  of 
red  or  yellow,  it  is  most  annoying  to  get  a  print  of  a  homo¬ 
geneous  blackness,  simply  because  our  plate  is  practically  in¬ 
sensitive  to  even  the  palest  of  the  red  or  yellow.  The  diffi¬ 
culty  also  is  great  with  an  ordinary  plate  where  we  have  either  a 


106 


PRACTICAL  PHOTOMICROGRAPHY. 


dense  yellow  object  on  a  pure  white  ground, or  a  very  pale  yel¬ 
low  or  pink  of  such  a  nature  that  the  contrast  between  object 
and  ground  is  very  small.  Color- correct  photography  helps  us 
out  of  all  these  troubles  and  many  besides ;  and  it  may  be 
stated  once  more,  as  it  has  been  stated  by  the  writer  on  former 
occasions,  that  no  branch  of  photography  has  been  so  much 
benefitted  by  “  ortho-chromatics  ”  as  photo-micrography,  and 
that  in  color-correct  photography  lies  the  future  of  photo¬ 
micrography.  The  writer  has  lately  produced  such  renderings 
of  double  stained  pathological  subjects,  prepared  without 
regard  to  photographic  requirements,  as  a  few  years  ago  neither 
he  nor  any  other  person  would  have  been  mad  enough  to 
attempt. 

The  advances  that  up  to  this  date  have  been  made  in  ortho¬ 
chromatics  may  be  summed  up  briefly  in  the  statement  that 
our  plates  have  been  rendered  more  sensitive  to  yellow-greens, 
yellows,  oranges  and  reds  than  they  could  be  made  formerly, 
and  less  proportionately  sensitive  to  blue-greens,  indigos,  blues 
and  violets.  Plates  have  even  been  prepared  as  sensitive  to 
yellow  as  to  blue ;  but  our  usual  procedure  is  to  make  a  plate 
more  sensitive  to  yellows,  etc.,  than  an  ordinary  plate,  and  a 
little  less  sensitive  to  violets  and  blues,  and  to  assist  the  action 
when  necessary  by  calling  off  more  or  less  of  the  blue  and 
violet  by  means  of  yellow  “  screens.”  By  this  method  we 
have  more  command  over  our  results  than  if  our  plates  were 
as  sensitive  to  yellow  as  to  blue ;  indeed,  if  we  carried  the 
sensitiveness  too  far  into  the  red  end  of  the  spectrum,  we 
should  often  have  to  cut  off  some  of  our  yellow  rays,  and  we 
should  have  great  difficulty  in  finding  a  suitable  light  whereby 
to  develop  our  plates.  Still,  for  a  few  subjects,  a  greater 
sensitiveness  to  red  would  be  a  great  boon,  though  developing 
difficulties  would  multiply. 

In  Britain,  at  least,  color-correct  gelatine  bromide  plates 
may  be  bought ;  as  a  rule,  they  keep  quite  well  for  a  few 
weeks,  but  we  prefer  to  use  them  within  a  few  days.  Mr.  B. 
J.  Edwards,  working  under  the  “  Tailfer-Clayton  ”  patent, 
produces  plates  orthochromatized  by  an  eosin  process ;  Mr. 
J.  R.  Gotz  trades  in  plates  sent  from  Germany  by  Vogel  and 


PRACTICAL  PHOTOMICROGRAPHY. 


107 


Obernetter.  The  best  color-correct  plates  for  photo-microg¬ 
raphy  we  have  ever  used  were  produced  by  Mr.  Edwards  for 
copying  purposes.  Where  sensitiveness  to  certain  regions  of 
the  red  is  required,  the  “  azaline  ”  plates  of  Obernetter  are, 
perhaps,  the  best  in  the  market ;  but  “  cyanin”-stained  plates 
are  the  best  of  all  for  reds. 

The  photo-micrographer  who  has  time  and  a  good  drying 
cupboard  may  quite  easily  orthochromatize  his  own  plates. 
An  emulsion  should  be  chosen  capable  of  giving  ample 
density,  not  very  rapid,  and  not  containing  more  than  3 
parts  of  iodide  to  100  of  bromide.  The  writer  has  tried,  per¬ 
haps,  every  published  process  of  any  promise  for  “  staining  ” 
his  plates,  but  finds  none  so  simple  or  so  effective  as  a  process 
lately  promulgated  by  the  talented  Mr.  Ives,  of  Philadelphia. 
The  dyes  suggested  by  Mr.  Ives  are  erythrosin  and  cyanin. 
The  latter  seems  to  sensitize  for  reds  more  than  any  aniline 
we  have  tried,  but  the  operations  must  be  carried  out  prac¬ 
tically  in  total  darkness.  The  erythrosin  or  cyanin  may  be 
used  as  follows : 


Take  of  the  dye . 1  grain 

Absolute  alcohol. . . 4  ounces 


Soak  the  plate  in  this  for  one  minute,  allow  to  dry  in  total 
darkness.  This  will  not  take  long.  Then  place  the  plate 
face  upwards  in  a  black  tray  and  cover  the  tray  with  another 
tray  or  flat  cover  having  a  hole  in  the  top  into  which  is  let  a 
piece  of  tubing.  Connect  the  tubing  with  the  water  tap  and 
wash  the  plate  in  the  covered  tray  for  five  to  ten  minutes. 
In  very  subdued  red  light,  or  in  darkness,  convey  the  plate  to 
the  drying  press ;  when  dry  it  is  ready  for  use.  The  drying- 
box  or  press  must  be  properly  constructed  for  passing  a  con¬ 
stant  current  of  dry  air ;  details  of  such  presses  will  be  found 
in  “  The  Processes  of  Pure  Photography  ”  (Scovill  &  Adams 
Company). 

A  book  as  long  as  the  whole  of  this  one  would  be  required 
to  do  full  justice  to  the  processes  of  color-correct  photography. 
We  have  to  allow  for  such  wide  variations  of  color,  and  there 
are  so  many  different  methods  available  for  meeting  our  various 


108 


PRACTICAL  PHOTO-MICROGRAPHY. 


color  difficulties,  that  we  can  only  give  the  outlines  of  the 
principles  upon  which  we  work.  In  the  majority  of  cases  a 
color-correct  plate  is  almost  useless  unless  we  use  in  conjunction 
with  it  a  “  screen,”  but  it  must  be  remembered  that  if  we  are 
using  an  oil  light,  and  particularly  a  paraffin  lamp  without 
camphor  in  the  paraffin,  our  light  is  yellow,  and  to  a 
considerable  extent  acts  precisely  as  a  yellow  screen  would  do. 
It  is  necessary  to  have  several  yellow  screens  of  different  tints, 
and  it  is  well  to  have  also  one  or  two  screens  of  blue,  also  of 
varying  tints.  A  glass  of  a  color  known  as  “  signal  green  ” 
will  be  found  useful  for  pale  reds  of  which  eosin  stains  are 
types.  The  colored  glasses  called  “  screens  ”  ought  to  have 
their  sides  perfectly  parallel,  (ought  to  be  what  opticians  call 
“worked,”)  but  unless  the  screens  are  to  be  used  in  some 
critical  position  in  the  light  rays,  as  for  example  close  behind 
the  condenser,  we  do  not  insist  upon  this  perfection.  We  do 
not  find  that  it  matters  in  the  least  where  the  screen  is  placed 
so  long  as  it  is  between  the  light  and  the  object,  and  so  long  as 
no  light  reaches  the  object  except  such  as  passes  through  the 
screen.  The  colored  glass  may  be  put  in  a  holder  about  midway 
between  the  light  and  the  condenser.  If,  as  in  some  cases,  the 
screen  is  screwed  into  a  part  of  the  mounting  of  the  condenser 
(in  which  position  it  is  often  called  a  “light-modifier”),  then 
it  ought  to  be  “  worked  ”  glass.  A  set  of  most  useful  screens 
can  be  made  by  mixing  aurantia  with  collodion,  and  three 
screens  may  advantageously  be  made  in  this  way  by  mixing 
the  aurantia  in  three  different  proportions,  about  one  grain  of 
dye  being  first  dissolved  in  one  ounce  of  alcohol.  The  col¬ 
lodion  may  then  be  poured  upon  a  glass  plate,  which  has 
been  previously  thoroughly  cleaned,  and  then  rubbed  all 
over  with  French  chalk  (powdered  talc),  the  chalk  being 
apparently  all  removed  with  a  clean  dry  cloth.  If  desired,  the 
collodion,  which  must  be  in  an  even  film,  may  be,  after  drying 
stripped  from  the  plate  and  used  as  a  film,  or  the  edges  may 
be  varnished,  and  the  film  left  on  the  glass.  One  screen  should 
be  of  the  very  palest  color,  the  other  two  progressively  darker. 
At  need  any  two,  or  all  three,  may  be  used  together.  We  are 
indebted  to  Mr.  C.  H.  Bothamley  for  the  suggestion  of  aurantia. 


PRACTICAL  PHOTO-MICROGRAPHY. 


109 


Mr.  Wellington  recommends  an  alcoholic  solution  of  turmeric, 
and  a  solution  of  picric  acid  will  also  be  found  to  be  of  great 
service.  In  any  case  the  screens  must,  when  tested  by  aid  of 
a  spectroscope,  cut  off  some  portion  more  or  less  of  the  violet 
and  blue  of  the  spectrum. 

In  cases  where  we  have  blue  or  violet  lacking  actinic  contrast 
with  the  white  of  the  background,  or  likely  to  be  over-exposed 
before  other  colors  (as  yellow  or  red)  can  be  sufficiently  exposed, 
we  cut  off  some  blue  or  violet  by  use  of  our  screen,  and  the 
paler  is  our  violet  or  blue  the  darker  must  be  our  screen.  But 
if  our  violet  be  very  dark,  and  more  particularly  if  it  be  a 
reddish  violet,  such  as  logwood  shows  at  times,  we  shall  get  a 
better  result  in  presence  of  a  red  or  yellow-brown  contrast 
stain,  if  the  latter  be  pale,  by  omitting  the  screen  entirely, 
for  the  depth  of  the  violet  amounts  in  practice  to  so  much 
opacity,  not  to  mention  the  red  impurity  of  the  violet  stain. 
But  if  the  contrast  red  or  yellow  be  also  dark  the  screen  may 
be  required  unless  our  plate  be  very  much  corrected  for  color. 

It  is  not  an  uncommon  occurence  to  find  preparations  very 
faintly  stained  with  red,  and  it  is  still  more  common  to  find 
red  stains  and  also  yellow  fade  after  a  time.  In  such  a  case 
there  is  want  of  actinic  contrast  between  object  and  ground, 
and  the  latter  is  exposed  practically  as  fully  as  the  former,  and 
so  we  can  not  get  a  white  ground  in  our  positive.  In  such  a 
case  a  rather  dark  yellow  screen  used  either  with  an  ordinary 
or  an  orthocliromatic  plate  will  prove  of  great  service. 
Bacteriological  preparations  seem  to  be  specially  subject  to 
this  fading,  and  we  have  many  times  got  good  results  with  a 
yellow  screen  after  repeated  failures  without  one. 

Insect  preparations  and  others  similar,  where  we  have  yellows 
approaching  opacity  at  times  are  very  difficult.  Sometimes 
the  best  result  is  got  by  using  an  ordinary  plate  without  any 
screen,  sometimes  a  yellow-sensitive  plate  without  screen,  some¬ 
times  the  latter  plate  with  a  screen  added,  sometimes  a  cobalt 
blue  screen,  and  sometimes  a  signal  green.  The  best  procedure 
depends  upon  the  depth  and  quality  of  the  yellow  in  the  object. 
The  common  flea  as  usually  mounted  seems  to  come  out  best 
with  an  ordinary  plate,  but  we  possess  one  which  curiously 
enough  requires  not  only  a  yellow-sensitive  plate — which  pro- 


110 


PRACTICAL,  PHOTO-MICROGRAPHY. 


duces  differentiation  in  the  body-color  of  the  insect — but  a 
yellow  screen  which  prevents  the  background  from  being  over¬ 
exposed.  It  must  always  be  remembered  in  dealing  with 
orthochromatics  that  we  cannot  always  make  practice  agree 
with  theory,  and  the  only  way  to  succeed  with  some  objects  is 
to  “  ring  the  changes  ”  till  we  do  succeed. 

Without  color-correct  photography  it  would  be  found  well- 
nigh  impossible  to  photograph  any  thin  section  or  very  minute 
object  stained  lightly  with  .that  very  useful  dye,  gentian  violet. 
The  same  remark  applies  to  another  favorite  stain,  methyl  blue. 
Gentian  violet  used  with  an  orthochromatic  plate  in  presence 
of  a  yellow  screen,  or  illuminated  by  an  oil  lamp,  is,  in  our 
opinion,  the  most  satisfactory  stain  for  nearly  all  bacteria,  for, 
in  fact,  all  that  are  amenable  to  the  violet  stain.  And  methyl 
blue  is  a  very  useful  contrast  stain  for  such  micro-organisms 
as  we  choose  to  stain  red.  If  a  preparation  be  stained  with  a 
clear  violet  so  as  to  show  body-details  in  the  object,  or  if  a 
preparation  is  double  stained,  red  and  blue,  then  a  color-correct 
plate,  generally  helped  by  yellow  screen  or  yellow  light,  will 
give  renderings  quite  beyond  the  reach  of  an  ordinary  plate. 
This  we  have  verified  a  hundred  times. 

“  Test  ”  diatoms  are  sometimes  mounted  in  media  having 
very  high  refraction  indices  but  of  very  yellow  color.  We 
refer  to  certain  arsenic  compounds  used  for  the  mounting  of 
A  mphipleura  jpellucida  and  such  like.  Over  and  above  a  dif¬ 
ficulty  entailed  by  the  optical  principles  involved  when  we  are 
working  at  very  wide  numerical  apertures,  this  yellowness  of 
the  mounting  medium  makes  it  very  difficult  to  get  a  white 
background  in  our  print.  A  yellow-sensitive  plate  used  with¬ 
out  a  screen  frequently  lessens  the  difficulty  alluded  to  in  con¬ 
nection  with  the  background. 

In  concluding  this  chapter  we  can  only  say  that  while  we 
apologize  for  the  meagre  amount  of  definite  instruction  given 
by  us  under  this  head,  it  must  be  remembered  that  the  vari¬ 
eties  of  color  and  shade  are  almost  infinite ;  that  unfortunately 
language  is  not  sufficiently  accurate  to  permit  of  accurate  color 
nomenclature ;  and  lastly,  that  experience  alone  can  teach  us 
how  best  to  choose  a  suitable  plate  and  a  suitable  screen  for 
each  subject  as  it  falls  to  our  lot  to  photograph  it. 


PRACTICAL  PHOTO-MICROGRAPHY. 


Ill 


Our  latest  color  sensitizing  bath  is  due  to  Mr.  Bothamley, 
and  gives  considerable  sensitiveness  to  yellow,  but  not  to  red. 
The  general  sensitiveness  of  the  plate  is  raised  about  three 
times,  and  the  aptitude  for  giving  density  greatly  increased. 
No  washing  is  required,  and  the  plates  keep  well.  A  rather 
slow  plate  should  be  chosen,  and  the  caution  about  proportion 
of  iodide  must  be  kept  in  mind.  The  proper  erythrosin  is 
that  of  the  Badische-anilin-and-soda-fdbrih ,  called  “  Erythro¬ 
sin  B.”  The  use  of  ammonia  in  this  way  is  covered  by  patent 
in  England.  The  ammonia  may  be  omitted,  but  five  or  six 
times  more  exposure  will  be  required.  (Bothamley.) 


Erythrosin  solution  (1  to  1000) .  1  part. 

Ammonia  (1  to  10) .  1  part. 

Distilled  water  . .  8  parts. 


Bathe  the  plate  for  two  minutes.  Dry.  No  washing  needed. 


PART  II.— PRINTING  PROCESSES. 


INTRODUCTORY. 

* 

It  is  hardly  within  onr  scope,  and  it  is  certainly  not  our  in¬ 
tention,  to  enter  here  at  any  great  length  into  printing  processes. 
After  a  negative  has  been  obtained  the  process  of  producing  a 
print  or  prints  is  purely  photographic,  and  full  instructions  for 
printing  by  the  many  processes  available  are  to  be  found  in 
many  purely  photographic  books ;  for  example,  the  reader 
will  find  ample  instruction  on  the  subject  in  the  book  already 
repeatedly  alluded  to :  “  The  Processes  of  Pure  Photography,” 
by  Professor  Burton  and  the  present  writer,  forming  one  of 
the  series  of  publications  of  which  the  present  book  forms 
another  item. 

Still  by  attention  to  certain  details  in  the  ordinary  photog¬ 
raphic  processes  points  preeminently  important  to  the  photo- 
micrographer  may  be  emphasized,  and  our  present  instructions 
shall  tend  to  work  chiefly  upon  points  affecting  specially  the 
printing  of  a  photo-micrographic  negative. 

The  processes  we  propose  to  treat  thus  briefly  are : 

The  albumen  paper  silver  process . 

The  gelatine  chloride  emulsion  process. . . . 

The  gelatine  bromide  emulsion  process. . . . 

The  platinotype  process . 

Enlarging  on  bromide  paper. 

Lantern  slides  by  contact  and  by  reduction. 


Paper  prints  by 
contact. 


CHAPTER  XVII. 


PRINTING  ON  ALBUMENIZED  PAPER. 

This  process  is  the  one  most  commonly  used  by  photogra¬ 
phers  for  producing  their  prints  in  the  ordinary  course  of 
work  ;  for  our  purpose  it  is  well  adapted,  as  it  lends  itself  to 
the  rendering  of  fine  details  in  a  fairly  satisfactory  manner ; 
the  image  is  not  lost  and  made  granular  by  being  deposited  in 
the  texture  of  the  paper  as  in  some  other  processes ;  but  the 
very  finest  details  either  in  shadows  or  in  high  lights  are  apt 
to  be  lost  in  the  operations  of  “  toning  ”  and  “  fixing,”  how¬ 
ever  carefully  these  operations  may  be  performed.  Shadow 
details  are  greatly  emphasized  and  generally  improved  by  the 
process  of  enamelling,  to  which  we  shall  call  attention  at  the 
end  of  this  chapter. 

Paper  of  special  quality  is  coated  by  special  machinery  with 
albumen  containing  a  certain  amount  of  chloride,  usually  am- 
monic  or  sodic.  This  is  floated  upon  a  solution  of  argentic 
nitrate  and  by  double  decomposition  argentic  chloride  is 
formed  and  remains  in  the  albumen  layer  with  a  certain  neces¬ 
sary  excess  of  argentic  nitrate.  Argentic  chloride  in  such 
conditions  darkens  under  the  action  of  white  light ;  the  black 
parts  of  a  negative  prevent  access  of  light  to  the  parts  of  the 
sensitive  paper  in  contact  with  the  negative,  the  light  parts  of 
the  negative  allow  the  light  to  pass  and  affect  the  paper,  and 
so  a  “  print  ”  is  obtained.  The  print  thus  obtained  if  not 
“fixed  ”  would  soon  turn  black  all  over,  so  it  must  be  fixed  in 
sodic  hypo-sulphite,  but  this  would  leave  the  print  with  a  very 
unpleasant  color,  so  before  fixing  we  “tone”  the  print  by 
causing  a  layer  of  gold  to  be  deposited  over  the  image ;  this 
gold,  being  deposited  over  the  peculiar  gradations  of  color 
proper  to  the  reduced  chloride  and  albuminate  of  silver,  gives 
various  color  or  “  tones  ”  according  to  the  color  of  the  sub- 


116 


PRACTICAL  PHOTO-MICROGRAPHY. 


jacent  image  and  the  fineness  of  division  of  the  gold  itself. 
The  fixing  operation  does  not  remove  the  tone  produced  by  the 
gold ;  and,  moreover,  the  gold  imparts  to  the  image  an  ability 
to  withstand  atmospheric  and  other  actions  which  but  for  the 
gold  would  soon  destroy  the  beauty  of  the  image. 

The  paper  is  almost  always  bought  ready  albumenized  and 
“  salted,”  and  very  frequently  ready  sensitized  also ;  in  the 
latter  case  special  processes  are  resorted  to  in  order  to  make 
the  paper  keep  good  for  a  period  of  weeks  or  even  months. 
W e  prefer  the  ready  sensitized  paper  for  general  work,  and  in 
Britain  it  is  easily  obtained  at  very  reasonable  prices. 

If,  however,  sensitized  paper  cannot  be  obtained,  the  albu¬ 
menized  salted  paper  is  to  be  floated  albumen  downwards  in  a 
bath  of  argentic  nitrate.  (See  page  64.)  Time  of  floating 
3  to  5  minutes  according  to  temperature  and  nature  of  the 
albumenized  paper.  The  higher  the  temperature  the  shorter 
should  be  the  flotation. 

The  “  bath  ”  formulated  on  page  64  should  be  neutral  or 
slightly  alkaline,  and  must  be  kept  up  to  strength,  for  of  course 
each  sheet  of  paper  floated  on  it  removes  a  certain  quantity  of 
silver. 

When  the  negatives  are  “  thin,”  full  of  detail  but  lacking 
contrast,  the  60-grain  bath — or  a  strong  bath — should  be  used 
and  full  time  of  flotation  given.  “  Hard  ”  negatives  may  be 
printed  on  lightly  sensitized  paper,  that  is  to  say  on  paper 
floated  on  a  weak  bath,  and  only  long  enough  to  ensure  com¬ 
plete  conversion  of  the  salt  in  the  paper  into  silver  salt.  The 
ready  sensitized  papers  usually  give  more  brilliant  prints,  or 
more  contrast,  than  paper  sensitized  at  home  and  used  imme¬ 
diately  without  “  preservatives.” . 

A  hard  negative  is  best  printed  in  direct  sunlight ;  a  very 
thin  negative  should  be  printed  in  weak  light,  or  in  brighter 
light  behind  a  sheet  of  ground-glass. 

When  flotation  is  finished,  the  sheet  of  paper  is  to  be  hung 
up  in  a  cool  dry  place  to  dry ;  nothing  must  touch  the  face 
while  it  is  damp,  and  the  corners  should  not  be  allowed  to  curl 
inwards  and  so  spoil  the  centre  of  the  sheet.  It  is  well  to  blot 
off  each  sheet  as  it  leaves  the  sensitizing  bath,  having  allowed 


PRACTICAL  PHOTO-MICROGRAPHY. 


117 


the  sheet  to  drip  as  much  as  it  will.  Pure  bibulous  paper  must 
be  used  for  this  purpose.  If  the  sheet  after  drying  is  placed 
between  sheets  of  blotting  or  pure  filter  paper  previously  im¬ 
pregnated  with  sodic  carbonate  and  dried,  it  will  remain  white 
and  good  for  weeks.  Sensitizing  and  drying  must  be  per¬ 
formed  in  yellow  or  artificial  light.  All  these  matters  are  most 
carefully  treated  in  “  Practical  Guide  to  Photographic  and 
Photo-mechanical  Printing  Process  ”  by  W.  K.  Burton,  C.  E. 
(London,  Marion  and  Co.)  and  also  in  the  book  already  alluded 
to  in  the  Scovill  Photographic  Series. 

The  negative  is  laid  face  upwards  in  a  “  printing  frame  ” 
(fig.  30.)  and  on  it  is  laid  the  albumenized  paper  face  down- 


Fig.  30. — Printing  Frame. 

wards,  so  that  the  albumen  surface  is  in  contact  with  the 
gelatine  film.  The  frame  is  then  taken  to  the  daylight  and 
printing  commences.  As  a  rule  photo-micrographic  negatives, 
if  thoroughly  good,  take  longer  to  print  than  ordinary  photo¬ 
graphic  negatives.  In  any  case  the  printing  must  be  carried 
considerably  beyond  the  stage  when  the  print  seems  to  look  at 
its  best,  as  seen  by  opening  one-half  of  the  hinged  back  of  the 
printing  frame.  The  operations  of  toning  and  fixing  greatly 
lessen  the  depth  attained  by  the  merely  exposed  print. 

When  a  batch  of  prints  are  printed,  having  after  printing 
been  stored  away  in  some  suitable  light-tight  receptacle,  we 
proceed  to  the  operations  of  toning,  fixing,  and  washing. 

The  prints  are  first  immersed  in  water,  being  well  covered 
therein  and  kept  moving  and  separate  from  each  other.  After 


118 


PRACTICAL  PHOTOMICROGRAPHY. 


about  ten  minutes  they  are  moved  into  a  fresh  supply  of  water. 
If  the  paper  is  “  ready  sensitized  ”  this  second  water  should 
contain  a  small  dose  of  sodie  carbonate  sufficient  to  neutralize 
the  acidity  of  such  paper.  If  the  paper  is  home-made,  and  if 
it  is  not  brick  red  on  entering  the  second  water,  a  pinch  of 
common  salt  (sodic  chloride)  must  be  added  to  the  second 
water.  The  prints  must  go  into  the  toning-bath  red,  not  violet 
or  purple.  As  a  rule  the  print  should  pass  through  four 
changes  of  water  before  being  toned. 

The  toning-bath  preferred  by  us,  the  only  one  we  think  it 
necessary  here  to  give  will  be  found  on  page  64.  It  is  to  be 
poured  into  a  white  perfectly  clean  flat  dish  large  enough  to 
hold  two  prints  side  by  side,  and  deep  enough  to  allow  one 
print  to  slip  easily  under  another.  The  temperature  of  the 
toning-bath  should  be  about  65  deg.  Fahr.,  not  under  60  deg. 
nor  over  70  deg.  The  prints  are  put  in  face  downwards  and 
kept  moving.  The  Toning  Solution  must  be  alkaline  ;  an  acid 
toning  solution  is  the  commonest  of  all  amateurs’  printing 
troubles.  The  prints  ought  in  from  ten  to  twenty  minutes  to 
change  from  brick  red  to  a  handsome  color,  brown,  purple,  or 
warm  blue-black  according  to  taste  and  time.  (Prints  always 
turn  a  little  more  blue  after  drying.)  Home  sensitized  paper 
usually  tones  more  quickly  than  ready  sensitized.  It  is  an  ad¬ 
vantage  to  get  as  much  gold  as  possible  deposited  without  turn¬ 
ing  the  prints  blue  ;  that  amounts  to  our  saying  that  it  is  better 
to  tone  slowly  than  quickly.  If  the  bath  is  too  strong  in  gold 
the  prints  turn  blue  very  quickly,  but  the  blue  is  only  superficial 
and  comes  away  in  the  fixing  bath  leaving  the  print  practically 
untoned.  A  fairly  good  rule  is  to  stop  the  toning  when  the 
print  has,  seen  by  reflected  light,  a  good  color  inclined  to  be 
warmer  than  we  desire  our  finished  print ,  seen  by  transmitted 
light  just  a  suspicion  of  blueness  in  the  half  tones  of  the  higher 
lights. 

After  toning,  the  prints  are  put  into  clean  cold  water  and 
there  kept  moving  if  possible.  A  trace,  however  slight,  of 
hypo  in  the  toning  solution  ruins  it,  the  greatest  care  is  there¬ 
fore  to  be  exercised  to  keep  these  solutions  apart.  The  toning 
bath  should  seldom  be  filtered,  but  gold  chloride  must  be  added 


No.  1.— B.  Anthracis  in  Blood.  X  750. 


No.  2.— Spermatozoa  of  Triton,  X  1000. 


Platk  IV. 


PRACTICAL  PHOTO-MICROGRAPHY. 


119 


to  replace  the  quantity  taken  out  by  the  prints,  and  each  time 
gold  is  added  the  bath  should  be  tested  for  acidity  and  alkalized 
slightly  if  necessary.  The  gold  salt  is  usually  sold  in  sealed 
tubes  containing  fifteen  grains ;  one  of  these  tubes  may  be 
scratched  with  a  file,  put  into  a  two-ounce  bottle,  the  tube  broken 
and  water  added  to  fill  the  bottle.  One  dram  of  this  contains 
about  one  grain  of  gold  chloride,  and  a  sheet  of  paper  (17x22 
inches)  may  be  expected  to  take  up  about  one  grain  of  gold  salt. 

From  the  fresh  water  after  toning  the  prints  are  to  be  put 
into  a  fixing  bath  of  sodic  hyposulphite,  made  decidedly  alka¬ 
line,  as  on  page  64.  In  this  they  are  to  be  kept  separate,  in 
motion,  and  for  a  period  ranging  from  12  to  18  minutes.  A 
very  light  print  may  be  removed  in  case  of  need  after  8  or  10 
minutes.  The  prints,  if  on  “  double  albumenized  ”  paper — a 
quality  having  a  high  gloss — are  to  be  put  direct  from  the 
hypo  bath  into  water  containing,  to  each  pint,  about  an  ounce 
of  common  salt ;  this  is  to  prevent  blisters,  which  are  apt  to 
occur.  Then  the  prints  must  be  very  thoroughly  washed,  an 
easy  matter  if  the  proper  means  be  taken,  a  very  difficult  one 
if  commercial  washing  machines  are  the  only  apparatus  used. 
Our  plan  is  to  lay  each  print  down  on  a  slab  of  glass  or  vul¬ 
canite  under  a  rose  tap,  and  to  pass  a  squeegee  many  times 
briskly  over  the  back  of  the  print,  occasionally  turning  the 
print  face  upwards  to  get  some  water,  but  not  any  squeegeeing, 
of  course. 

After  a  few  changes  of  water  and  applications  such  as  this,  one 
of  the  washing  machines  may  be  trusted  to  finish  the  elimina¬ 
tion  of  the  hypo,  in  four  to  six  hours  ;  the  water  running  con¬ 
stantly  and  being  syphoned  oft  from  the  bottom  of  the  washing 
trough.  After  thorough  washing,  the  prints  may  be  dried  or 
blotted  off,  but  before  they  are  quite  dry  they  should  be  rolled 
one  by  one,  face  outwards ,  round  a  ruler  or  other  roller  of  hard 
wood,  and  there  left  till  they  Sre  dry,  or  till  they  retain  the 
outward  curl. 

The  effect  of  glazing  or  enamelling  the  face  of  a  print  is  to 
produce  an  appearance  not,  perhaps,  artistic,  but  in  some  cases, 
such  as  ours,  desirable.  The  shadow  details  are  greatly  assisted 
by  this  gloss.  The  simplest  way  we  know  to  impart  a  gloss  to 
the  albumen  print  is  to  place  the  print,  washed  but  still  wet. 


120 


PRACTICAL  PHOTO-MICROGRAPHY. 


with  its  face  in  contact  with  a  sheet  of  “  ferrotype  plate  ”  hav¬ 
ing  a  highly  glazed  impervious  surface.  If  the  ferrotype 
plate  is  clean  the  print,  as  it  dries,  will  leave  the  plate  either 
spontaneously  or  with  very  slight  assistance.  A  plate  of  glass 
rubbed  with  pure  talc  powdered  (French  chalk)  may  be  used 
instead  of  the  ferrotype  plate.  A  still  higher  glaze  may  be 
obtained  thus :  Make  a  solution  of  good  gelatine  £  to  1  ounce, 
water  10  ounces.  Swell  the  gelatine  in  the  water,  then  dissolve 
by  heat.  Take  a  sheet  of  glass,  free  from  scratches,  clean  well, 
sprinkle  over  with  powdered  talc  from  a  pepper  box  or  muslin 
bag.  Rub  the  talc  all  over  ;  then  all  (apparently)  off.  Coat 
the  plate  with  plain  collodion.  When  the  collodion  is  set,  but 
not  dry,  wash  it  under  a  tap  or  in  changes  of  water  till  the 
greasy  appearance  is  gone.  Place  the  collodionised  plate  face 
upwards  in  a  flat,  clean  dish,  containing  the  melted  gelatine, 
submerge  the  print  to  be  enamelled  face  upwards  in  the  gela¬ 
tine,  bring  plate  and  print  up  together  face  to  face ;  put  a 
sheet  of  waterproof  cloth  over  the  print  and  carefully  squeegee 
the  print  to  the  collodion  surface  of  the  glass  plate,  avoiding 
air  bells.  Allow  to  dry,  run  a  knife  edge  round  the  edges  of 
the  print,  when  it  will  probably  jump  from  the  glass  with  a  very 
highly  glazed  surface.  The  drier  the  print  at  time  of  strip¬ 
ing  the  higher  will  be  the  gloss.  It  is  not  absolutely  necessary 
to  immerse  the  plate  in  the  gelatine  solution ;  if  the  print  is 
thoroughly  saturated  with  the  solution,  it  may  be  laid  down 
on  the  collodionised  glass  and  then  squeegeed. 

If  these  enamelled  prints  are  to  be  mounted  on  cards,  it  is 
well  to  pass  a  card  of  no  great  thickness  through  hot  water  and 
to  place  it  behind  the  print  on  the  glass,  while  the  print  is  still 
saturated  with  gelatine,  and  then  to  squeegee  all  together, 
placing  a  flat  board  on  back  of  the  card  after  squeegeeing  and 
leaving  a  weight  on  the  board  for  a  considerable  time,  to  pre¬ 
vent  the  card  from  bending  away  from  the  print. 

If  the  reader  propose  to  mount  his  own  prints  of  every  de¬ 
scription,  he  will  probably  find  fresh  starch  paste  as  convenient 
and  as  efficient  as  any  mountant.  Pour  a  little  cold  water  on 
the  starch,  make  a  thick  cream  with  it,  then  add  hot  water. 
Flour  paste  must  never  be  used.  Gelatine  dissolved  in  water 
and  spirits  is  with  some  a  favorite  mountant. 


CHAPTER  XVIII. 


GELATINE  CHLORIDE  PAPER. 

By  some  manufacturers  paper  is  coated  with  emulsion  of 
gelatine  chloride  (argentic)  with  a  certain  excess  of  argentic 
organic  salt,  and  paper  so  prepared  is  used  for  “  printing-out  ” 
in  a  manner  very  similar  to  albumen  paper.  (The  term  “  print¬ 
ing-out”  is  used  to  signify  a  process  wherein  the  image  is 
revealed  by  the  action  of  light  alone,  in  contradistinction  to 
the  term  “  printing  by  development,”  where  after  light-action 
the  image  is  wholly  invisible  or  only  faint,  and  development  is 
required  to  bring  the  image  to  its  full  vigor.) 

The  practice  of  printing  the  gelatine-chloride  paper  is  pre¬ 
cisely  similar  to  the  practice  with  albumen  paper.  A  few 
details  of  difference  may  be  noted  as  to  the  properties  of  the 
papers.  The  gelatine-chloride  paper  gives  much  more  contrast 
than  ordinary  albumenized  paper,  so  where  we  have  thin  weak 
negatives  the  former  offers  a  great  advantage.  The  gelatine 
paper  seems,  as  a  rule,  to  lose  as  much  depth  in  operations 
following  printing,  but  seems  to  require  a  considerably  larger 
quantity  of  gold  chloride  to  produce  the  toning  effect.  The 
printing  of  the  gelatine  paper  is  usually  more  rapid  than  that 
of  the  albumen  paper. 

After  printing  with  Dr.  Liesegang’s  paper  no  washing  is 
required,  but  the  prints  are  at  once  toned  in  a  bath  made  thus : 


Water . 24  ounces 

Sodic  hyposulphite . 6  ounces 

Ammonic  sulpho-cyanide . 1  ounce 

Saturated  aqueous  solution  of  potash  alum . 2  ounces 


Dissolve,  and  place  in  the  solution  some  scraps  of  gelatine- 
chloride  paper  for  about  24  hours.  Filter,  then  add  : 

Water .  6  ounces 

Auric  terchloride  . 15  grains 

Ammonic  chloride . 80  grains 


122 


PRACTICAL  PHOTOMICROGRAPHY. 


This  bath  tones  and  fixes  at  one  operation.  To  judge  of  the 
color  we  must  look  through  the  print,  reflected  light  will  mis¬ 
lead  us.  It  is  not  easy  to  overtone  by  this  process. 

Obernetter’s  Aristotype  paper  has  in  our  hands  worked  best 
with  separate  toning  and  fixing  baths. 


Toning  Solution. 

Ammonic  sulpho-cyanide . 140  grains 

Sodic  phosphate . 140  grains 

Sodic  tungstate . 100  grains 

Water . 24  ounces 

Dissolve.  Put  in  scraps  of  paper  as  above,  filter,  then  add  : 

Auric  terchloride . 15  grains 

Water .  4  ounces 


Tone  to  a  rich  brown  color — or  into  blue  if  desired — then, 
after  washing,  fix  in  weak  hypo  ;  viz. : 

Hypo .  1  part 

Water . 10  parts 

These  papers  may  be  dried  with  their  natural  surface  or 
may  be  highly  glazed  by  squeegeeing  to  ferrotype,  vulcanite, 
talced  glass,  or  oollodionized  talced  glass,  as  described  in  last 
chapter. 


i 


CHAPTER  XIX. 


PRINTING  ON  BROMIDE  PAPER. 

This  printing  process  is  on  the  whole,  perhaps,  the  most 
satisfactory  and  convenient  of  all  for  the  photo-micrographer. 
The  author  always  produces  by  this  process  prints  intended  for 
special  purposes  of  exhibition,  which  is  a  fair  guarantee  of  his 
own  opinion,  at  least. 

The  photo-micrographer  whose  time  is,  perhaps,  pretty  fully 
occupied  with  other  business  will  find  the  bromide  paper 
process  convenient  from  its  celerity,  and  satisfactory  on  account 
of  the  beauty  of  the  results  that  by  a  little  practice  may  be 
obtained.  There  are  certainly  difficulties  in  the  process,  but 
as  they  will  all  be  overcome  by  care  and  practice,  they  need 
not  appal  us. 

The  process  is  one  of  exposure — to  artificial  light  as  a  rule — 
and  development,  by  ferrous  oxalate  generally.  There  is  no 
protracted  period  of  printing,  no  watching  of  the  progress  of 
printing,  no  toning  nor  serious  washing  before  fixing. 

To  attain  speedily  to  success,  and  to  ensure  repetition  of  success 
with  the  same  or  similar  negatives,  the  worker  should  in  the 
first  place  obtain  a  standard  fight.  A  u  regulator  gas-burner  ” 
or  an  oil  lamp  always  turned  to  the  same  height,  or  a  standard 
candle,  or  a  fixed  length  of  magnesium  ribbon,  or  wire,  or  a 
“  unit  lamp,”  any  of  these  is  suitable.  W e  may  also  fix  either 
a  standard  distance  from  the  radiant,  varying  our  exposure,  or 
we  may  fix  upon  a  standard  exposure,  and  vary  our  distance 
from  the  radiant.  Our  own  preference  is  to  have  a  normal 
distance  from  fight  to  sensitive  surface  of,  say,  18  inches,  and 
to  vary  the  exposure  according  to  our  negative,  and  this 
practice  we  recommend  to  beginners,  though  the  more 
experienced  will  find  a  marked  advantage,  without  introducing 
insuperable  difficulties,  in  varying  both  distance  and  exposure 


124 


PRACTICAL  PHOTOMICROGRAPHY. 


to  meet  certain  peculiarities  of  negative.  In  varying  tlie 
distances,  however,  we  must  not  overlook  the  law  regarding 
the  intensity  of  light,  viz  :  that  the  intensity  varies  inversely 
as  the  squares  of  the  distances  between  radiant  and  recipient ; 
in  other  words  that  halving  the  distance  is  equivalent  to 
quadrupling  the  exposure.  If  the  correct  exposure  at  18  inches 
be  twenty  seconds,  at  30  about  55  seconds  will  be  required,  as 
182  :302  20:55$. 

If  magnesium  ribbon  be  used  it  will  be  found  convenient  to 
burn  each  time  a  definite  length,  say  one  inch,  and  to  vary  the 
distance  of  the  printing  frame  from  the  burning  wire.  A 
number  of  prints  may  be  exposed  at  one  operation  with 
magnesium  wire  by  arranging  the  frames  in  a  circle,  or  at 
various  parts  of  several  circles,  either  imaginary  or  actually 
traced  on  the  table. 


Fig.  31. 


By  such  an  arrangement  as  shown  at  figure  31  we  may 
evidently  expose  with  one  length  of  wire  or  ribbon,  burned  ai 
“  X,”  eight  negatives  of  three  grades  of  density  at  one  time. 

“  Bromide  paper,”  as  it  is  usually  called  by  photographers, 
is  a  good  quality  of  paper  coated  with  an  emulsion  of  gelatine- 
bromide  of  silver,  a  considerable  proportion  of  chloride 


PRACTICAL  PHOTO-MICROGRAPHY. 


125 


being  sometimes  added.  The  sensitiveness  of  the  emulsion 
varies  in  different  makers’  products,  but  it  is  usually  consider¬ 
ably  higher  than  any  collodion  emulsion,  and  always  lower 
by  a  good  deal  than  that  of  such  gelatine  bromide  plates  as  are 
used  for  the  production  of  negatives.  In  order  that  the  paper 
may  not  curl  and  become  unmanageable  in  aqueous  solutions, 
the  gelatine  film  ought  to  be  very  thin ;  and  to  counterbalance 
its  thinness  it  ought  to  contain  a  high  proportion  of  the  argentic 
salts,  otherwise  vigor  of  image  will  be  difficult  to  attain. 

The  paper  is  placed  face  to  face  with  a  negative  in  a 
frame  in  the  usual  way  for  contact  printing,  but  this  opera¬ 
tion  must  be  performed  in  non-actinic  light,  a  simple  yellow 
glass  not  being  sufficient  protection  against  daylight,  nor  even 
against  ordinary  artificial  light.  If  there  is  any  doubt  as  to 
which  is  the  face — or  gelatine  side — of  the  paper,  it  may  be 
laid  down  for  a  few  moments  on  a  flat  surface,  and  it  will 
soon  show  signs  of  curling  face  inwards.  Makers  usually 
send  out  three  qualities  of  bromide  paper :  A — Thin  paper 
with  a  surface  glossy ;  B — Thicker  paper  with  surface  glossy ; 
C — Thick  paper  with  a  mat  surface,  which  is  not  recommended 
for  our  purpose.  The  sensitiveness  does  not  appear  to  be 
affected  in  any  way  by  the  surface,  all  grades  being  practically 
alike  sensitive. 

The  development  is  usually  effected  by  ferrous  oxalate,  me 
constituents  being  used  in  the  proportions  of  from  4  to  6  parts 
of  the  potassic  oxalate  to  1  part  of  the  ferrous  sulphate  (see 
page  63).  We  recommend  the  addition  of  at  least  one-half 
a  grain  of  soluble  bromide  to  each  ounce  of  developer. 

We  have  assumed  a  standard  light  and  a  standard  distance 
from  light  to  printing  frame.  We  now  remark  regarding 
exposure : 

A  dense  negative  requires  long  exposure,  and  vice  versa. 

Long  exposure  tends  to  softness,  detail,  want  of  contrast. 

Short  exposure  tends  to  brilliance,  contrast,  pluck. 

Over-prolonged  exposure  leads,  as  a  rule,  to  an  unpleasant 
color,  a  greenish  tint,  which  is  undesirable. 

Too  short  exposure  leads  to  “  chalk  and  soot,”  dense  black 
shadows,  and  glaring  whites. 


126 


PRACTICAL  PHOTOMICROGRAPHY. 


A  strong  developer  (say  4  oxalate  to  1  iron)  gives  good 
brisk  blacks,  a  weak  developer  (say  1  to  1)  is  apt  to  yield 
“washed  out”  tones  of  the  image,  while  a  very  weak  developer 
sometimes  produces  a  peculiar  appearance  of  measliness  or 
grain. 

If  we  have  to  print  a  weak,  “  ghostly  ”  negative,  we  keep 
down  the  exposure  and  develop  with  a  brisk  developer 
restrained  with  a  full  dQse  of  free  bromide,  say  1  grain 
bromide  per  ounce  of  developer.  If  our  negative  is  hard  or 
shows  violent  contrast,  we  give  a  prolonged  exposure  and  use 
a  developer  consisting  of,  perhaps,  1  part  of  iron  to  6  of 
potassic  oxalate,  and  even  to  this  some  water  may  be  added, 
while  the  free  bromide  may  be  reduced,  or  even  omitted. 

One  strong  point,  perhaps  the  strongest  point  in  favor  of 
this  process  is  that  it  lends  itself  above  all  other  printing  pro¬ 
cesses  to  the  production  of  good  prints  from  inferior  negatives, 
and  enables  us  to  vary  to  a  very  marked  extent  the  prints  we 
may  obtain  from  any  one  negative.  A  negative  showing  little 
more  than  a  ghost  of  an  image  may  be  made  to  yield  a  print 
actually  “  hard while  a  negative  of  the  “  chalk  and  soot  ” 
order  may  be  made  to  yield  a  print  of  the  utmost  softness,  and 
these  effects  may  be  produced  by  a  mere  variation  of  the  ex¬ 
posure,  assisted  or  unassisted  by  intelligent  variation  of  devel¬ 
opment. 

The  manipulation  of  bromide  paper  is  simple.  After  the 
exposure  the  sheet  of  paper  is  plunged  into  clean  water  in  such 
a  manner  as  +to  prevent  formation  of  air  bells ;  if  bubbles  do 
occur  they  are  easily  seen  and  must  instantly  be  removed  by 
hand  or  with  a  clean  camel  hair-brush.  As  soon  as  the  paper 
lies  flat  in  the  dish  it  may  be  transferred  face  upwards  to  the 
developing  dish,  or  if  the  same  dish  is  to  be  used  for  both 
operations  of  soaking  and  washing,  the  water  only  requires  to 
be  poured  out  of  the  first  dish  and  the  paper  left  in  it  face  up¬ 
wards.  The  ferrous  oxalate  developer  is  now  poured  over  the 
paper.  (See  page  92.)  The  developer  should  be  allowed  to 
act  until  the  shadows  of  the  picture  show  a  good  pronounced 
black  as  seen  by  the  subdued  colored  light  of  the  operating 
room.  By  this  time  the  highest  lights  should  not  show  any 


PRACTICAL  PHOTO-MICROGRAPHY. 


127 


grayness,  while  the  half-tones  should  be  from  pale  to  dark  gray 
according  to  their  nature.  In  our  work  there  ought  always  to 
be  some  part  of  the  picture  perfectly  white  when  development 
is  complete,  but  often  it  is  impossible  to  attain  this ;  our  best 
guide  then,  remains  in  the  vigorous  tone  of  the  dark  parts. 
With  the  developer  we  have  given  on  page  92  the  image 
ought  not  to  begin  to  appear  for  at  least  20  seconds,  and  devel¬ 
opment  with  fresh  solution  may  be  expected  to  finish  in  about 
two  to  three  minutes.  Yery  rapid  development  points  to  over¬ 
exposure,  which  is  probably  the  most  serious  error  that  in  our 
special  work  can  be  committed. 

As  soon  as  development  is  complete,  the  print  is  to  be 
flooded  with  acidulated  water,  not  plain  water.  A  dram  of 
acetic  acid  (glacial)  to  one  pint  of  water  will  do,  or  a  dram  of 
citric  acid.  If  the  water  smells  of  acetic  acid  it  will  suffice. 
Three  applications  of  acid  water  for  a  minute  or  so  each  will 
suffice  to  wash  out  most  of  the  iron,  the  print  being  moved  in 
the  acid  water  all  the  time  ;  washing  in  plain  water  till  the 
acid  is  eliminated  follows,  and  then  the  print  is  fixed  in  the 
ordinary  bath  of  hypo,  1  part,  water  5  parts  made  alkaline. 
In  this  the  prints  should  stay  at  least  twenty  minutes,  then 
they  are  washed  in  the  manner  detailed  for  albumen  prints. 
(Page  119.) 

The  Eastman  Company  of  Rochester,  U.  S.,  prepare  not 
only  bromide  papers  of  the  very  highest  quality,  but  also  a 
modification  called  Transferotype  Paper.  For  the  photo- 
micrographer  “Transferotype”  is  a  most  valuable  process. 
The  printing  and  other  processes,  up  to  and  including  the  final 
washing,  are  exactly  the  same  as  for  ordinary  bromide  paper, 
but  as  in  transferotype  the  sensitive  emulsion  (insoluble)  is  laid 
over  a  soluble  stratum  of  gelatine  on  the  paper,  it  is  evident 
that  by  dissolving  the  soluble  gelatine  we  can  remove  the 
paper.  If  we  can  stick  our  image-bearing  film  to  a  transparent, 
or  semi-transparent,  or  translucent  support,  as  glass  or  opal, 
and  then  remove  the  paper,  it  is  evident  that  we  can  produce 
a  transparent  or  translucent  positive — reversed  as  regards  right 
and  left  certainly,  but  for  us  this  reversal  is  of  no  import. 

By  the  following  means,  then,  we  can  produce  by  “  Trans- 


128 


PRACTICAL  PHOTOMICROGRAPHY. 


fer”  a  lantern-slide,  transparent  positive,  or  “opal  print.” 
After  the  final  washing,  which  in  the  present  case  need  not  be 
so  very  laborious  as  if  no  further  ablution  were  to  take  place, 
we  place  our  transferotype  print  face  to  face  with  a  perfectly 
clean  sheet  of  glass  or  opal,  squeegee  the  two  together,  place  a 
double  layer  of  blotting  paper  over  the  print,  then  a  flat  piece 
of  wood,  then  on  the  wood  a  slight  weight,  as  ‘one  pound. 
After  about  half  an  hour  we  place  the  support  bearing  the 
print  in  water  at  about  100  deg.  Fahr.  or  higher,  and  soon  the 
paper  will  float,  or  may  be  carefully  lifted  off.  The  film  is 
then  washed  under  the  tap,  getting  a  gentle  rubbing  with  the 
soft  pads  of  the  fingers  if  necessary  to  remove  any  gelatine 
adhering  to  the  picture ;  acidified  alum  may  follow  this  wash¬ 
ing.  (See  formula  on  page  63.)  After  the  cleaning  with 
alum  the  plate  is  finally  washed,  dried  and  varnished  with  a 
clear  varnish  usually  called  “  crystal  varnish.” 

Bromide  papers  “  A  ”  and  “  B  ”  may  have  a  greater  or 
smaller  amount  of  glaze  conferred  on  them  by  one  of  the  fol¬ 
lowing  methods.  A  fairly  glazed  surface  may  be  obtained  by 
squeegeeing  the  finished  and  washed  prints  to  a  sheet  of  vulcan¬ 
ite.  When  dry  they  will  come,  or  may  be  taken  from  the 
vulcanite,  and  will  have  a  very  good  glossy  surface.  Talced 
glass  may  be  used  in  place  of  the  vulcanite.  Or  glass  talced 
and  collodionized  as  on  page  120  may  be  used,  and  this  will 
not  only  give  a  very  high  gloss  but  will  tend  to  protect  the 
surface  from  scratches  and  from  damp. 

Transferotype  prints  may  be  dried  naturally  and  the  paper 
removed  at  any  future  time.  Previous,  in  such  a  case,  to 
squeegeeing  to  the  rigid  support,  the  prints  must  be  very  thor¬ 
oughly  wetted  in  water,  and  they  must  not  have  undergone 
alum  treatment.  Bromide  prints  and  transferotype  prints 
may  be  developed  with  pyro,  and  by  some  workers  the  pyro- 
developer  is  used  with  a  view  to  warmer  tones.  The  hydro- 
quinone  developer  as  formulated  on  a  later  page  (page  1 52) 
answers  most  admirably  for  bromide  prints  and  also,  of  course, 
for  transferotypes  ;  for  bromide  prints  on  “A,”  “  B,”  or  “  C” 
paper  we  consider  the  hydroquinone  developer  superior  in 
certain  respects  to  all  other  developers;  the  regularity  of 


PRACTICAL  PHOTO-MICROGRAPHY. 


129 


development,  the  scope  allowed  for  variations  in  exposure, 
provided  the  exposure  has  been  sufficient ,  and  the  color  of  the 
deposit  or  image,  lead  us  to  recommend  this  developer  with 
much  confidence.  But  the  pyro  and  hydroquinone  develop¬ 
ers  so  act  upon  the  soluble  substance  of  transferotype  paper  as 
to  make  the  stripping — not  by  any  means  impossible  nor  even 
difficult — but  less  easy  than  after  ferrous  oxalate  development. 

The  image  on  bromide  or  transferotype  paper  can  by  various 
proceedings  after  fixation  be  toned  to  various  colors ;  for 
details  of  these  matters  we  must  refer  our  reader  to  general 
photographic  literature. 

The  method  of  developing  bromide  papers  for  enlargements 
and  transferotype  paper  for  lantern  slides  is  practically  identical 
with  the  method  we  have  given  in  this  chapter. 

Bromide  paper  offers  a  vastly  greater  prospect  of  permanence 
of  result  than  other  silver  printing  processes  ;  in  fact  a  bromide 
paper  print  produced  with  proper  precautions  is  in  point  of 
permanence,  as  it  is  in  point  of  beauty,  inferior  to  no  purely 
photographic  print  that  at  present  we  know  how  to  produce. 

A  very  pretty  effect  may  be  produced  by  attaching  a  number 
of  transferotype  prints,  arranged  in  an  artistic  manner,  to  a 
sheet  of  opal.  The  prints  being  trimmed  with  scissors  to  the 
desired  shapes  are,  in  the  bath  of  plain  water  after  fixing  and 
washing,  caused  to  adhere  to  the  opal  plate  in  their  desired 
positions.  The  plate  bearing  the  prints  is  in  the  usual  way 
removed  from  the  water  and  the  prints  are  carefully  squeegeed 
into  perfect  contact.  The  prints  are  then  allowed  to  dry ,  and 
the  stripping  in  hot  water  performed  thereafter. 


CHAPTER  XX. 


THE  PLATINOTYPE  PROCESS. 

^  This  is  a  process  due  mainly  to  the  ingenuity  and  chemical 
skill  of  Mr.  W.  Willis,  of  London,  England,  and  is  so  far  pro¬ 
tected  by  patent  laws  that  in  this  country  the  original  platino- 
type  process  can  only  be  worked  under  license  from  the  com¬ 
pany,*  and  with,  for  the  most  part,  materials  provided  by  the 
company.  The  process  has  a  strong  claim  on  our  attention  on 
account  of  its  almost  indubitable  permanence,  the  image  con¬ 
sisting  of  metallic  platinum,  and  on  account  of  the  great  beauty 
of  its  results  under  favorable  conditions.  On  these  two  accounts 
we  think  it  right  to  give  at  least  a  brief  description  of  the  pro¬ 
cess  ;  but  except  for  special  micrographic  purposes — and  these 
practically  of  one  class — we  do  not  put  forward  this  process  as 
•  eminently  suited  to  the  photo-micrographer.  Where  extreme 
fineness  and  definition  of  detail  is  a  necessity  no  printing  pro¬ 
cess  by  which  the  image  is  deposited  in  the  substance  of  a 
textile  such  as  paper,  can  be  expected  to  compete  with  a  pro¬ 
cess  whereby  the  image  is  kept  on  the  surface  and  prevented 
from  “  losing  itself  ”  among  the  fibres  of  the  textile  by  a 
surface-medium  such  as  albumen  or  gelatine.  But  where 
fineness  of  detail  and  sharpness  of  outline  are  secondary, 
and  indubitable  permanence  paramount  considerations,  this 
platinotype  process  is  to  be  strongly  recommended  when  the 
negatives  are  of  high  technical  quality.  But  unless  the 
negatives  are  tolerably  good  in  a  technical  sense,  i.  e.  un¬ 
less  they  show  a  considerable  range  of  gradation  from  high 
light  to  shadow,  and  unless  they  possess  a  reasonable  amount 
of  “  pluck  ”  or  contrast,  their  rendering  as  printed  in  platino¬ 
type  will  not  be  satisfactory  nor  even  tolerable. 


*We  understand  that  this  license  is  now  unnecessary. 


PRACTICAL  PHOTOMICROGRAPHY. 


131 


The  image  in  platinotype  printing  becomes  under  the  action 
of  light  visible ;  with  the  Platinotype  Company’s  original 
process  of  image  becomes  rather  faintly  visible,  with  a  new 
process  lately  introduced  from  Germany,  the  image  “  prints 
right  out.”  With  the  latter  process,  known  as  Pizzighelli’s, 
all  that  is  required  is  to  print  the  image  to  the  required  depth 
and  then  to  “  clear”  it  with  a  weak  dilution  of  hydrochloric 
acid.  The  Company’s  ordinary  paper  is  partly  printed  and 
partly  developed. 

For  the  Hot-bath  Development  process :  The  paper  is  ob¬ 
tained  from  the  company  ready  sensitized,  it  must  be  kept 
away  from  light  and  perfectly  dry.  In  order  that  it  may  be 
kept  quite  dry  it  should  be  placed  in  a  calcium  tube,  a  light- 
and-air-tight  tube,  having  at  one  end  a  receptacle  containing 
calcic  chloride  in  some  shape.  Sometimes  the  paper  is  bought 
separately  and  the  materials  for  sensitizing  separately  ;  in  such 
cases  full  instructions  accompany  the  goods.  By  means  of 
varying  the  proportions  of  certain  ingredients  of  the  sensitizer, 
we  may  vary  our  results  within  limits  or  prepare  a  paper 
more  suitable  than  the  ordinary  commercial  article  to  our 
negatives. 

Every  precaution  must  be  taken  with  this  paper  to  prevent 
it  getting  damp  in  the  least  degree.  A  sheet  of  India-rubber 
is  put  behind  the  paper  and  preferably  overlapping  it  in  the 
printing  frame.  Printing  is  carried  on  till  the  shadows  take  a 
very  peculiar  dirty  green  brown  .color,  or  until  all  the  details 
are  faintly  visible  over  the  print,  except,  in  a  few  cases,  in  the 
very  highest  lights.  After  printing,  the  paper  must  again  be 
stored  with  every  precaution  against  light  and  damp.  Any 
veil  produced  by  light  in  this  process  is  not,  as  in  the  albumen 
process,  removed  by  the  after  operations  of  toning  and  fixing, 
for  in  platinotype  there  is  no  analogous  “  clearing  ”  action. 
Therefore  the  progress  of  printing  must  be  examined  in  the 
frame  as  rapidly  as  possible,  and  it  may  be  noted  that  the 
process  of  printing  is  much  more  rapid  with  platinotype  than 
with  ordinary  albumen  paper. 

To  develop  platinotype  prints.  Make  a  saturated  aqueous 
solution  of  potassic  oxalate  at  60  degrees  Fahr.,  and  heat  to 


132 


PRACTICAL  PHOTO-MICROGRAPHY. 


about  160  degrees  in  an  enamelled  flat  iron  dish,  a  Bnnsen  or 
other  burner  serving  to  keep  the  temperature  up  while  a  suc¬ 
cession  of  prints  are  developed.  On  this  hot  solution  made 
alkaline  the  print  is  laid  for  a  few  seconds ;  the  previously 
pale  image  will  almost  instantly  flash  into  a  black  picture,  the 
high  lights  remaining  for  the  time  yellow.  If  the  printing 
or  exposure  has  been  too  short  the  developing  solution  should 
be  hotter,  say  180  degs.,  if  the  exposure  was  too  long  the 
bath  should  be  more  cool,  say  110  degs.  It  will  generally 
be  found  best  to  expose  to  such  an  extent  that  the  develop¬ 
ment  will  be  correct  at  160  degs.  We  usually  have  slightly 
acidified  the  bath  with  oxalic  acid  and  got  fine  results,  but 
the  Company  now  recommend  that  the  bath  be  kept  faintly 
alkaline. 

After  development,  which,  conducted  as  above,  will  not  oc¬ 
cupy  more  than  15  or  20  seconds  even  with  a  “ cool”  solution 
such  as  suggested,  the  print  is  to  be  put  straight  into  : 


Water, . . .  60  parts. 

Hydrochloric  Acid, .  1  “ 


Two  more  baths  of  the  same  ingredients  are  to  follow,  and 
the  third  bath  must  never  show  any  yellow  tinge  ;  if  it  does 
show  such  a  tinge  it  must  be  followed  by  a  fourth  bath.  When 
No.  1  bath  becomes  very  yellow  it  should  be  rejected  and  the 
others  be  advanced  each  a  step,  No.  2  becoming  No.  1,  etc. 
After  the  baths  the  prints  are  to  be  washed  for  about  15 
minutes  in  running  water  to  remove  the  acid  ;  they  are  then 
finished. 

Pizzighelli’s  paper  requires  no  development,  but  at  time  of 
printing  it  must  be  slightly  damp,  not  wet.  To  damp  it  we 
may  breathe  on  it  or  put  it  into  a  box  in  company  with  pieces 
of  wet  blotting  paper.  Printing  may  be  partly  performed  by 
light,. and  finished  with  cold  solution  : 


Saturated  Solution  Sodic  Carbonate .  5  parts. 

Distilled  Water, . 100  “ 


Clearing  is  performed  as  above. 

The  latest  process  put  forward  by  the  Platinotype  Company 
is  convenient  and  good.  The  company  send  out  with  the  paper 


PRACTICAL  PHOTO-MICROGRAPHY. 


133 


not  only  a  salt,  the  nature  of  which  they  do  not  state,  but  the 
platinum  salt  which  is  not  in  this  case  present  in  the  paper  at 
first.  Full  instructions  are  given  with  the  paper,  and  these 
directions  are  so  complete  and  accurate  that  failure  is  unlikely 
if  the  negatives  be  suitable  for  the  process.  The  printing  is 
performed  in  a  frame  and  by  daylight,  as  before,  but  after  the 
printing,  the  paper  is  caused  to  take  up  a  certain  amount  of 
moisture,  which  it  readily  does  on  exposure  in  a  damp  apart¬ 
ment  or  box,  the  damping  and  the  printing  being  kept  in 
certain  relations  to  each  other.  Then  follows  development  on 
the  “  cold  bath,”  which  gives  the  name  to  this  process.  Devel¬ 
opment  is  less  rapid  than  with  the  hot  bath;  in  fact,  the  print 
having  been  floated  for  a  moment  or  two  on  the  cold  develop¬ 
ing  solution  is  usually  thereafter  held  in  the  hands  till 
development  is  seen  to  be  complete.  The  clearing  process  in 
acid  and  the  washing  are  as  in  the  hot  bath  process. 


CHAPTER  XXI. 


ENLARGING. 

This  is  a  somewhat  important  subject  to  the  photo-micro- 
rapher,  as  it  is  frequently  inconvenient  to  take  at  the  first  a 
negative  as  large  as  may  ultimately  he  required.  “  Enlarging,” 
as  the  word  is  technically  used  by  photographers,  will  not,  as 
some  persons  seem  to  think,  help  us  to  get  any  superior  quali¬ 
ties  to  those  which  we  can  get  by  direct  amplification  properly 
managed,  excepting  only  the  one  quality  of  size.  If  we  have 
to  produce  a  photograph  of  an  uneven  diatom  exempli  gratia , 
at  a  magnification  of  300  diameters,  we  shall  get  it  just  as 
well,  or  better,  by  direct  operation  in  the  camera  as  by  magni¬ 
fying  to  150  diameters  in  the  camera,  and  then  “enlarging” 
to  300  diameters,  always  provided  that  in  our  original  direct 
operation  we  do  not  overtax  our  instruments.  By  “  enlarge 
ment  ”  we  enlarge  and  accentuate  the  difference  of  focal 
planes  in  the  original  object  just  as  much  as  we  accentuate  it 
by  direct  projection  ;  and,  what  is  more,  we  often  introduce 
new  aberrations  in  our  system  of  “  enlargement,”  unless  we 
are  tolerably  au  fait  in  our  optics  and  careful  in  our  operations. 

In  considering  enlargement  we  have  two  optical  systems  to 
attend  to.  1st.  A  system  for  collecting  light  and  transmitting 
it  through  our  original  negative  or  positive,  or  for  concentrat¬ 
ing  the  light  passing  through  our  original  at  or  near  a  certain 
point  with  reference  to  our  projecting  system.  2d.  Our  pro¬ 
jecting  system,  which  regulates  the  sizes  of  our  enlarged  image 
and  projects  it  upon  our  sensitive  surface. 

Our  condensing  or  transmitting  system  depends  chiefly  upon 
the  sensitiveness  of  our  photographic  receiving  surface  ;  if  the 
latter  is  very  sensitive  and  our  light  reasonably  actinic,  we 
require  no  condenser  at  all.  But  if  either  our  receiving  surface 


PRACTICAL  PHOTO-MICROGRAPHY. 


135 


is  little  sensitive  as  albumen  paper,  or  our  radiant  little  actinic 
as  an  oil  lamp,  then  in  practice  we  require  an  optical  system 
known  as  a  condenser. 

As  we  propose  to  treat  of  two  methods  only  of  enlarging  we 
shall  touch  but  lightly  on  the  subject  of  condensers.  Our 
purpose  is  to  confine  ourselves  to  the  use  of  such  sensitive 
materials  as  gelatine-bromide  emulsion,  in  which  case  we  use 
daylight  reflected  or  diffused,  and  transmitted  in  parallel  • 
pencils  through  the  original ;  or  failing  daylight,  artificial  light 
concentrated  and  transmitted  in  converging  pencils  through 
the  original  to  a  certain  point  at  or  near  the  optical  centre  of 
the  projecting  system. 

Enlarging  by  Daylight. 


Fig.  32. 

The  cut  (Fig.  32)  shows  almost  at  a  glance  an  arrangement 
which  if  carried  out  in  a  reasonably  workmanlike  manner,  will 
fulfil  every  desideratum  for  enlargement  by  ordinary  diffused 
daylight.  C  is  a  camera  capable  of  holding  in  its  dark  slide 
the  negative  from  which  we  propose  to  make  an  enlarged  print 
on  paper  or  glass.  C  is  fixed  in  any  convenient  manner  to  the 
sides  of  an  aperture,  A,  in  a  wall  or  shutter  preferably  facing 
the  north.  F  is  a  reflector  of  white  blotting  paper  or  any  mat 
white  surface,  not  a  mirror  nor  any  shiny  surface ;  E  is  an 
easel  sliding  easily  along  the  base-board  D  ;  E  must  keep  at  all 
times  parallel  to  the  negative  in  the  camera,  and  to  start  with 


136 


PRACTICAL  PHOTO-MICROGRAPHY. 


the  centres  of  negative,  projecting  lens  and  easel  should  all  be 
in  one  line.  If  we  are  to  project  our  image  upon  paper — as 
bromide  paper — the  paper  is  simply  fixed  by  drawing  pins  to 
E ;  if  our  enlargement  is  to  be  on  glass,  E  must  have  a  rebate 
or  other  contrivance  to  carry  the  glass  so  that  it  (the  glass)  shall 
occupy  precisely  the  position  of  the  surface  upon  which  we 
focus  our  projected  image.  The  writer  has  a  square  aperture 
«cut  in  E ;  in  this  aperture  he  places  a  sheet  of  ground  glass,  so 
that  (no  light  entering  the  apartment  except  through  the 
negative  and  lens)  he  can  arrange  and  focus  his  image  with 
perfect  ease  and  absolute  precision.  A  pane  of  non-actinic 
glass,  or  a  sheet  of  non-actinic  paper,  may  be  used  to  illuminate 
the  apartment  which  otherwise  should  be  dark.  This  pane 
should  be  covered  while  focusing  is  performed.  In  place  of 
the  angled  reflector  F  a  sheet  of  ground  glass  may  be  used 
parallel  to  the  negative,  and  a  few  inches  behind  it ;  tissue 
paper  will  answer  the  same  purpose. 

The  only  remarks  necessary  about  the  projection  lens  are  that 
it  should  be  capable  of  covering  at  full  aperture  the  whole  of 
the  area  of  negative  requiring  enlargement.  But  we  strongly 
recommend  the  use  of  a  lens  of  focal  length  as  long  as  possible, 
so  that  only  the  central  rays  of  its  “  cone  ”  are  used.  The 
only  real  limit  to  this  is  the  length  of  the  base-board  D  ;  and 
the  easel  E  may  be  on  wheels,  or  on  a  car  on  the  floor  of  the 
apartment.  This  lens  ought  also  to  be  a  doublet  lens,  one  of  the 
so-called  “Rectilinear”  or  “Symmetrical”  lenses  used  in 
photography.  If  it  have  a  sufficiently  great  focal  length  it 
need  not  be  stopped  down  at  all,  as  we  have  to  deal  with 
parallel  surfaces,  and  “  depth  of  focus  ”  does  not  come  into 
requisition. 

If  it  is  inconvenient  to  have  an  entire  apartment  darkened 
for  this  purpose,  figure  33  will  suggest  an  alternative. 

Here  we  have  two  cameras  joined  in  a  very  simple  manner, 
the  small  one  carrying  the  negative  from  which  we  desire  the 
enlargement,  the  dark  slide  of  the  larger  camera  carrying  the 
sensitive  material.  In  this  arrangement  we  are  likely  to  be 
troubled  by  want  of  stretch  in  the  large  camera  which  will 
entail  a  short  focus  projection  lens,  this  again  will  entail 


No.  2.  — Flagellated  Spirilla  (?  Serpens).  X  800. 


Plate  V. 


PRACTICAL  PHOTO-MICROGRAPHY. 


137 


stopping  down  of  the  projection  lens  which  will  entail  greatly 
prolonged  exposure.  The  usual  “  motions  ”  of  the  large  camera 
“rise  and  fall”  and  “traverse”  of  the  front,  will  enable  us  to 
arrange  our  image  on  the  ground-glass ;  while  the  small  camera 
carrying  the  negative  will  by  its  rack  and  pinion  enable  us  to 
arrange  the  magnification.  The  focusing  of  course  is  done  on 
the  ground-glass,  and  with  the  rack  and  pinion  of  the  large 


camera.  The  small  camera’s  back  is  pointed  towards  the  light, 
and  an  angled  reflector,  or  ground-glass  “diffuser”  is  used  as 
before.  With  this  arrangement  there  may  be  a  difficulty  in 
focusing  due  to  want  of  light ;  in  this  case  plain  glass  may  be 
substituted  for  ground-glass,  and  the  focusing  done  with  an 
eye-piece  of  the  Ramsden,  or  “  Zeiss  Aplanat  ”  type. 


138 


PRACTICAL  PHOTO-MICROGRAPHY. 


In  enlarging,  as  in  most  photographic  processes,  the  crux  of 
the  whole  affair  is  the  exposure,  and  it  is  just  as  hopeless  here 
for  us  to  attempt  to  give  rules  for  all  conditions  as  it  is  else¬ 
where.  All  we  can  say  is  that  cceteris  paribus  exposure  varies 
directly  as  diameters  of  enlargement.  That  is  to  say  :  with  a 
given  negative,  given  light,  given  lens,  given  diaphragm,  and 
given  sensitive  material,  it  will  take  twice  as  much  exposure  to 
enlarge  a  quarter  plate  to  S-|  x  6f  as  it  will  take  to  enlarge  it  to 
6^  x  The  best  way  is  to  make  a  trial  exposure — on  a  small 

piece  of  the  paper  and  at  the  distance  to  be  used  seriously — 
and  to  develop  it,  noting  carefully  our  remarks  as  to  the 
appearance  on  development  of  under  and  over-exposed  prints 
under  the  appropriate  headings.  AVith  an  arrangement,  as 
shown  in  Tig.  32,  and  an  average  negative,  using  a  13-inch 
rectilinear  at  full  aperture  {£)  and  Eastman’s  bromide  paper,  the 
daylight  being  of  average  autumn  quality,  to  enlarge  three 
diameters  the  writer  exposes  from  five  to  six  minutes  with 
ground  glass  diffuser,  rather  less  with  white  reflector  alone. 
But  his  average  photo-micrographic  negative  is  a  dense  one 
compared  with  a  landscape  negative,  not  to  mention  a  portrait 
one.  If  the  lens  has  to  be  stopped  down  to  prevent  spherical 
aberration,  the  exposure  will  be  greatly  increased,  generally 
double  for  each  next  smaller  size  of  stop  as  sent  out  by  opticians. 

A  “  table  of  enlargements  ”  will  be  found  in  this  book,  and 
with  it  the  worker  may  easily  reckon  approximately  the  posi¬ 
tion  of  lens  and  easel  for  any  given  operation.  The  camera 
bearing  the  lens  may  at  any  rate  be  racked  to  the  desired  ex¬ 
tent,  and  then  the  focusing  may  be  accurately  performed  by 
sliding  the  easel.  The  front  motions  of  the  camera  may  be 
used  to  arrange  the  image  suitably  on  the  screen.  Focusing, 
if  not  done  from  behind  with  ground  glass  as  suggested,  may 
be  done  by  viewing  the  projected  image  on  a  white  sheet  of 
paper  afterwards  to  be  replaced  by  the  sensitive  paper  or  glass, 
but  in  our  experience  the  former  method  is  vastly  superior. 

Enlarging  by  optical  lantern :  This  is  perhaps  the  favorite 
system  among  amateurs  who  are  likely  to  possess  an  optical 
lantern  for  its  ordinary  use.  Some  of  the  laws  touching  the 
optics  of  this  system  must  be  noticed. 


PRACTICAL  PHOTO-MICROGRAPHY. 


139 


In  the  first  place,  an  artificial  light  is  used,  and  that  light 
not  remarkably  powerful  or  actinic  in  comparison  with  day¬ 
light,  and,  moreover,  the  light  is  used  in  a  lantern  and 
not  many  inches  distant  from  the  original  which  is  to  be 
enlarged.  So  in  the  absence  of  a  condenser  we  should  have  not 
only  a  weak  but  an  uneven  light,  for  the  margins  of  our 
original  would  be  much  less  strongly  lighted  than  the  centre. 
We  here  give  a  cut  which  will  explain  the  functions  of  a  con¬ 
denser. 


A  is  the  radiant ;  B ,  a  condenser  of  two  elements  ;  C,  the 
original  negative  or  positive  held  in  frame  E ;  the  front  focus 
of  the  condenser  falls  at  a  point  inside  a  doublet  lens  1 ),  the 
rays  having  passed  through  the  original,  except  some  marginal 
rays  which  might  be  used  but  are  stopped  by  portions  of  the 
frame  E. 

Theoretically  the  radiant  should  be  a  point,  and  that  point 
accurately  in  the  focus  of  the  condenser.  Practically  we  can¬ 
not  get  such  a  point,  the  electric  arc  approaches  most  nearly 
to  a  point,  the  oxy-hydrogen  mixing-jet  lime-light  next,  a 
“blow-through”  lime-jet  perhaps  next,  and  so  on  down  to  the 
worst  of  all — a  multiple-wicked  oil  lamp.  Still  even  the  three- 
wicked  lamp  may  in  practice  be  successfully  used,  especially  if 
we  adopt  an  ingenious  little  contrivance  due  to  Mr.  Traill  Taylor 
(Editor  of  the  British  Journal  of  Photography).  Mr.  Taylor’s 
suggestion  was  a  simple  converging  lens  placed  between  the 
light  and  the  condenser,  the  supplementary  lens  collecting  rays 
that  would  otherwise  not  reach  the  condenser. 

The  area  of  the  condenser  must  evidently  be  not  less  than, 
and  ought  to  be  greater  than,  the  area  of  the  portion  of  the 
original  we  propose  to  enlarge.  The  diameter  of  the  condenser 


140 


PRACTICAL  PHOTO-MICROGRAPHY. 


must  at  least  equal  tlie  diagonal  of  the  plate  or  portion  of  plate 
we  mean  to  enlarge.  Thus  the  ordinary  four-inch  condenser 
of  the  optical  lantern  is  not  of  sufficient  size  to  enlarge  an 
entire  quarter-plate.  Moreover,  the  larger  the  condenser  the 
more  light  it  will  collect,  so  that  the  exposure  required,  cceteris 
paribus ,  varies  inversely  as  the  area  of  the  condenser. 

In  practice  the  light  is  placed  as  nearly  as  possible  in  the 
focus  of  the  condenser,  the  negative  and  the  condenser  remain 
fixed  in  relation  to  each  other,  the  lens  for  projection  is  racked 
backwards  and  forwards  till  the  image  is  seen  sharp  on  a  trans¬ 
lucent  or  opaque  surface  placed  to  receive  the  image,  this  sur¬ 
face  being  parallel  to  the  original  undergoing  enlargement. 
The  easel  may  run  on  a  track,  or  may  be  on  castors,  we  figure 
a  most  convenient  form  of  arrangement  made  by  the  Eastman 
Company. 


Fig.  35. 

This  easel  may  very  aptly  be  used  for  daylight  enlarging  by 
our  first-described  process. 


PRACTICAL  PHOTO-MICROGRAPH Y. 


141 


The  front  of  the  lantern  must  be  so  arranged  that  the  lens 
used  for  projection  can  be  racked  to  at  least  twice  its  own 
focal  length  from  the  original. 

In  this  process  of  enlarging  (by  the  optical  lantern)  the  rela¬ 
tion  between  focal  length  of  the  projection  lens  and  area  of 
the  original  plays  no  part ;  a  diaphragm  is  of  little  optical 
advantage,  and  to  proper  selection  and  use  of  our  condenser 
we  must  look  for  success.  We  are  as  much  incompetent  here 
as  in  daylight  enlargement  to  give  rules  for  exposure,  but  the 
one  rule  we  did  give  holds  equally  good  here. 

If  by  either  daylight  or  lantern  process  we  wish  to  produce 
an  enlarged  negative ,  two  courses  are  open  to  us.  1st:  We 
may  make  from  our  original  (presumably  a  negative)  an  en¬ 
larged  positive,  and  from  that  we  may  print  “  by  contact  ”  a 
negative.  For  this  process  we  recommend  a  slow  gelatine- 
bromide  plate,  such  an  emulsion  as  is  made  for  lantern-slides 
answering  admirably ;  or  we  may  produce  our  large  contact¬ 
negative  by  the  carbon  process,  or  on  gelatine  chloride  emul¬ 
sion.  (For  the  carbon  process  consult  “  Processes  of  Pure 
Photography,”  or  u  Burton’s  Guide  to  Practical  Printing,”  etc.) 
This  is  probably  the  better  course  if  we  enlarge  by  daylight. 
2d :  We  may  in  the  first  place  make  a  small  positive  by  contact 
or  reduction  (according  to  the  size  of  our  original  negative), 
and  from  this  small  positive  we  may  make  an  enlarged  nega¬ 
tive  on  any  suitable  sensitive  plate  or  film.  A  small  positive 
such  as  would  be  a  good  lantern-slide  is  not  so  well  adapted 
for  this  purpose  as  one  almost  fogged  ;  that  is  to  say,  the  posi¬ 
tive  for  this  purpose  should  be  very  fully  exposed,  more  heavily 
developed  than  a  lantern -slide,  full  of  detail  without  absolutely 
clear  glass;  and  presenting  no  violent  contrasts. 

Whatever  be  the  sensitive  material  used  to  receive  the  en¬ 
largement,  the  after  operations  are  the  same  as  those  given  by 
us  under  the  heads  of  development,  etc.,  of  the  various  sensi¬ 
tive  materials  treated  in  other  chapters.  Bromide  paper  and 
Transferotype,  for  instance,  are  treated  just  as  if  they  had  been 
exposed  by  contact,  errors  in  exposure  will  manifest  them¬ 
selves  in  the  same  way  in  both  cases. 

If  very  sensitive  emulsion  is  used,  as  for  example  an  ordin- 


142 


PRACTICAL  PHOTO-MICROGRAPHY. 


ary  negative  gelatine  plate,  for  making  an  enlarged  negative, 
the  greatest  care  must  be  taken  to  prevent  extraneous  light 
reaching  the  sensitive  plate.  If  a  lantern  of  the  ordinary  type 
is  used  it  should  be  enclosed  in  a  box,  the  lens  only  protruding 
through  a  fitting  aperture. 

In  enlarging,  beautiful  effects  may  be  produced  very  simply 
by  judicious  “  vignetting”  ;  an  opaque  mask  having  a  suitably 
sized  and  shaped  aperture  cut  in  it  may  be  moved  towards  and 
from  the  sensitive  material  during  the  exposure.  Such  matters 
are  treated  in  most  books  devoted  to  photography. 


CHAPTER  XXII. 


LANTERN  SLIDES. 

It  is  almost  beyond  question  that  the  most  useful,  imposing 
and  satisfactory  method  by  which  we  can  exhibit  to  others  the 
result  of  our  micrographic  work,  lies  in  the  projection  of  a  posi¬ 
tive  image  upon  a  white,  and  proportionately  large,  surface  called 
the  “sheet”  or  “screen,”  by  means  of  an  Optical  Lantern. 

So  strongly  does  the  writer  feel  the  importance  of  this  subject 
that  he  proposes  to  devote  a  chapter  to  a  plea  for  the  use  of 
the  Lantern  for  many  purposes.  The  present  chapter  will  be 
devoted  to  a  description  of  certain  processes  which  seem  to 
the  writer  most  suitable  for  slide-making  in  the  hands  of  those 
who  are  not  thoroughly  conversant  with  this  branch  of  photo¬ 
graphy. 

It  is  necessary  in  the  first  place  to  know  precisely  what 
qualities  we  require  to  obtain  in  a  slide  so  that  it  may  be  a 
thoroughly  good  slide,  or  as  nearly  perfect  as  our  subject 
and  our  negative  will  allow. 

The  first  attribute  to  a  slide,  specially  of  a  photo-microgra¬ 
phic  slide,  is  perfect  clearness  of  the  ground.  Wherever  there 
is  no  subject  the  glass  must  be  quite  clear.  A  good  slide  laid 
down  on  a  sheet  of  white  paper,  will  show  the  paper,  seen 
through  the  ground  of  the  slide,  perfectly  white.  There 
should  in  such  condition  be  no  graying  or  degradation  of  the 
purity  of  the  white  in  the  paper. 

The  image  may  be  of  various  tones  according  to  the  process 
used,  but  it  must  always  be  “  plucky,”  and  never  pale  or 
“  washed  out,”  the  details  m  ust  stand  out  clearly  from  each 
other,  as  if  etched  with  the  finest  needle.  A  perfect  slide  is 
indescribable  but  once  seen  will  never  be  forgotten. 

The  image,  though  plucky,  must  not  be  opaque,  except 
where  the  detail  in  the  microscopic  image  was  opaque.  Such 


144 


PRACTICAL  PHOTO-MICROGRAPHY. 


an  image  as  that  of  amphipleura  pellucida  should  consist  of 
pure  white  and  absolute  opacity,  and  the  margins  of  black  and 
white  must  be  sharply  cut.  The  microscopic  image  is  really 
essentially  an  image  of  lines  and  points,  but  in  many  cases  we 
have  to  show  our  lines  so  blended  that  the  appearance  is  not  one 
of  lines  but  of  masses  resembling  the  masses  of  a  portrait  or 
landscape  photograph.  If  we  have  such  masses  in  a  slide, 
they  must  be  full  of  differentiation,  or  “  half  tone,”  as  it  may 
be  called ;  anything  approaching  opacity  here  will  be  fatal. 
As  instances  of  masses  we  may  cite  low  power  images  of 
insects,  physiological  preparations,  homogeneous  tissues  of 
any  kind,  “  resolvable,”  perhaps,  but  not  for  our  purpose 
“  resolved.”  All  such  masses,  then,  must  show  half  tone. 

Essential,  we  have  now  seen,  to  a  perfect  slide  are  :  Clear¬ 
ness  of  highest  lights  ;  opacity  of  resolved  lines  and  points ; 
half  tone  in  masses  ;  matter  of  taste  is  the  color  or  tone  ;  con¬ 
ventionally  fixed  is  the  size ;  and  “sharpness”  goes  without 
saying. 

It  is  necessary  that  the  argentic  deposit  forming  the  image 
be  very  fine,  partaking  more  of  the  nature  of  a  stain  than  of 
a  granular  deposit.  Makers  of  plates  for  slides  are  so  well 
aware  of  this,  and  the  processes  for  producing  suitable  emul¬ 
sion  for  slides  are  so  little  prone  to  yield  coarse  deposits,  that 
we  need  do  no  more  than  point  out  the  desideratum  of  a  fine 
grained  image.  But  on  this  account,  if  on  no  other,  gelatine 
bromide  emulsion  such  as  is  used  for  negative  production,  is 
as  a  rule,  totally  unsuited  for  slide  making  purposes. 

“  Wet  collodion”  stands  pre-eminent  among  processes  for 
the  production  of  photo-micrograpliic  slides ;  on  that  point  we 
have  no  doubt  whatever.  Perfect  clearness  of  lights,  complete 
opacity  of  lines  when  desired,  sharpness,  fineness  of  deposit, 
half  tone  in  masses — all  are  obtained  by  the  wet  collodion 
process  with  a  very  reasonable  exposure  in  the  camera;  for 
contact  printing  this  process  is  not  so  convenient.  But  in  any 
case  camera  copying  is  preferable  to  contact  printing  for  our 
special  purpose,  even  if  our  negative  is  the  same  size  as  our 
slide  is  to  be.  In  landscape  and  portrait  slides  a  warm  tone  is 
a  very  important  feature,  in  the  opinion  of  advanced  photog- 


PRACTICAL  PHOTO-MICROGRAPHY. 


145 


rapliers ;  in  pkoto-micrograpli y  tone  of  slide  is  a  very  subor¬ 
dinate  consideration,  if,  indeed,  a  black  tone  is  not  preferable. 

Dry  Collodion,  which  in  virtue  of  its  tone  is  perhaps  the 
most  suitable  of  all  processes  for  landscape  and  portrait  slides, 
gives  purity  of  high  lights  little  if  at  all  inferior  to  wet  collo¬ 
dion,  but  for  camera  copying  the  slowness  of  Dry  Collodion 
is  against  it. 

Gelatine-chloride  plates  are  most  valuable  for  contact  print- 
ing,  giving  great  clearness  and  varying  tones  at  will,  but  for 
camera  copying  their  excessive  slowness  is  very  unfavorable. 

Gelatine  bromide  plates  made  for  the  purpose  work  rapidly 
and  may  be  made  to  yield  clear  lights  and  good  tones ;  but 
while  assuredly  the  gelatine  bromide  process  is  the  most  con¬ 
venient,  and  while  its  results  under  suitable  conditions  are  in¬ 
ferior  to  none,  still  the  greatest  care  and  much  practice  are 
required  in  order  that  the  working  of  the  process  may  be 
mastered.  Foggy  slides  by  this  process  are  unfortunately  very 
common. 

We  have  now  put  the  merits  of  these  processes  fairly  be¬ 
fore  our  Reader.  If  he  makes  his  negatives  of  a  suitable  size 
for  contact  printing  we  recommend  on  the  whole  the  gelatine- 
chloride  process,  or  dry  collodion.  (The  latter  process,  how¬ 
ever,  we  must  not  detail  here  for  want  of  space.)  But  gelatine 
bromide  may  answer  to  perfection. 

For  camera  copying  we  strongly  recommend  the  wet  collo¬ 
dion  process,  but  as  we  fear  few  of  our  Readers  will  care  to 
face  its  difficulties,  or  rather  its  inconveniences,  we  give  as  an 
alternative  the  gelatine  bromide  process. 

The  usual  size  of  a  Lantern  Slide  plate  is  inches  square, 
as  a  rule  a  mask  is  placed  over  this  leaving  an  area  of  image 
of  about  2f  inches  diameter. 

To  print  by  contact ,  the  negative  is  placed  face  upwards  in 
a  printing  frame,  a  Lantern  Slide  plate  is  placed  face  to  face 
with  the  negative,  the  frame  closed  and  the  exposure  made  to 
the  light  in  the  usual  position,  i.  e.,  negative  next  the  light. 
It  is  advisable  that  the  extreme  edges  of  the  lantern  plate 
be  protected  from  the  light  by  a  mask  or  the  rebates  of  the 
printing  frame. 


146 


PRACTICAL  PHOTO-MICROGRAPHY. 


Reduction  or  copying  in  the  camera  may  be  performed 
most  conveniently  by  the  same  arrangement  as  is  figured  No. 
33  in  our  last  chapter.  The  negative  is  placed  in  the  “  dark 
slide  ”  of  the  large  camera ;  distance  is  arranged  by  the  rack 
and  pinion  of  the  large  camera,  centering  by  its  front  motions, 
while  the  lantern  plate  is  held  in  the  dark  slide  of  the 
smaller  camera  with  the  rack  of  which,  by  aid  of  an  eye¬ 
piece,  focusing  is  performed  in  the  usual  way.  The  back  of 
the  large  camera  bearing  the  negative  may  be  pointed  at  the 
sky,  may  be  lighted  by  an  angled  mat  white  reflector,  or  may 
have  a  sheet  of  ground  glass  or  tissue  paper  placed  parallel 
with  the  negative  and  a  few  inches  behind  it.  No  light  should 
get  past  the  edges  of  the  negative  into  the  large  camera,  but 
this  though  a  good  precaution  is  not  absolutely  essential. 

A  still  simpler  mechanism  consists  in  placing  the  negative 
against  the  pane  of  a  window,  lighting  the  negative  either  by 
a  reflector  or  by  the  sky,  and  photographing  it  to  the  slide  size 
in  an  ordinary  camera.  The  day  light  enlarging  apparatus 
figured  32  in  last  chapter  may  very  easily  be  utilized  for  our 
present  purpose,  by  simply  fixing  the  negative  in  the  window, 
turning  the  camera  round,  and  suppressing  the  easel.  The 
lens  used  must  be  rectilinear  and  may  have  a  focus  of  3£  inches 
or  upwards.  The  author  uses  a  “  Rectilinear  Stereo  ”  lens  of 
about  3|  inches  focus. 

The  Wet  Collodion  Process  for  Slides. 

In  most  books  of  photographic  instructions  that  have  any 
pretension  to  completeness,  an  account  of  the  wet  collodion 
process  will  be  found.  In  “  Processes  of  Pure  Photography  ” 
the  subject  is  treated  with  sufficient  care  to  enable  any  one 
referring  to  that  book  to  work  out  the  process  for  himself,  and 
to  succeed  with  the  process  for  our  present  purpose.  We  pro¬ 
pose  here  merely  to  accentuate,  as  it  were,  certain  directions 
given  in  the  book  alluded  to. 

Though  a  lantern-slide  is  only  three  and  one-quarter  inches 
square,  it  will  be  found  almost  necessary  to  use  a  larger  plate 
with  the  wet  process,  and  to  cut  it  down  after  the  slide  is  fin¬ 
ished.  Five  inches  by  four  will  be  a  suitable  size.  The  glass 


PRACTICAL  PHOTO-MICROGRAPHY. 


147 


must  be  very  good,  flat,  polished,  free  from  scratches,  bubbles 
and  other  visible  flaws.  The  glass  must  be  cleaned,  not  only 
in  the  usual  acceptation  of  the  word,  but  made  chemically 
clean  by  soaking  for  some  hours  in  dilute  acid  (say  nitric  acid 
1  part,  water  10  parts).  Thereafter  it  must  be  washed,  prefer¬ 
ably  under  a  tap  first,  and  then  with  a  solution  of  sodic  carbon¬ 
ate.  Next  it  should  be  well  rubbed  with  a  clean  cloth  dipped 
in  a  mixture  of  alcohol  and  ammonia  ;  lastly,  it  should  be  pol¬ 
ished  with  a  perfectly  clean  and  soft  chamois  leather.  For 
lantern  slides  we  do  not  recommend  any  substratum  of  al¬ 
bumen. 

The  collodion  may  be  bromo-iodised,  as  generally  sold  and 
used,  but  the  iodide  should  be  in  strong  proportion,  the  brom¬ 
ide  being  here  of  less  consequence.  The  collodion  should  be 
rather  limpid  than  thick,  and  should  be  moderately  ripe, 
neither  quite  fresh  nor  very  high-colored  with  age. 

The  “  silver  bath  ”  may  be  the  usual  35-grain  one,  and  must 
be  acid,  preferably  nitric  acid  being  used.  Of  course  this  bath 
must  have  the  usual  trace  of  iodine,  produced  by  immersion  of 
a  coated  plate  for  some  hours,  or  by  the  direct  addition  of  an 
iodide.  Either  the  flat  or1  the  dipping  bath  may  be  used,  per¬ 
haps  the  latter  is  here  preferable,  as  dust  must  be  most  zeal¬ 
ously  avoided.  Operations  of  coating  and  sensitising  are 
exactly  as  given  in  “  Processes  of  Pure  Photography,”  Chap¬ 
ter  YI. 

The  developer  may  be  the  usual  acid  ferrous  sulphate,  or 
the  ammonio-sulphate,  or  the  pyrogallol.  The  latter  devel¬ 
oper  requires  the  longest  exposure,  but  gives  magnificent 
results,  especially  if  used  with  a  collodion  containing  iodides 
only. 

Pyrogallol  Developer. 

Pyro .  2  grains 

Glacial  acetic  acid . 30  minims 

Water .  1  ounce 

Alcohol .  q.  s. 

This  solution  should  either  be  used  fresh,  or  the  pyro  dis¬ 
solved  in  alcohol  in  strong  stock  solution.  The  quantity  of 
aicohol,  which  should  be  of  good  quality,  depends  on  the  age 


148 


PRACTICAL  PHOTO-MICROGRAPHY. 

f 

of  the  silver  bath,  as  the  latter  is  more  and  more  nearly  satur¬ 
ated  with  the  collodion  solvents  of  the  immersed  plates,  the 
more  alcohol  will  be  required.  A  fresh  silver  bath  requires 
little  or  no  alcohol  in  the  developer. 

Ferrous  Sulphate  Developer. 

Proto-sulphate  of  iron,  fresh  green  crystals . 15  grains 


Nitric  acid .  1  minim 

Water .  1  ounce 

Alcohol . ; .  q.  s. 

Ammonio-Sulphate  Developer  (from  “  Processes”). 

Ammonio-sulphate  of  iron . 77  grains 

Acetic  acid  (glacial)  . 70  minims 

Water . 3  ounces 

Alcohol . q.  s. 


One  or  other  of  these  developing  solutions  is  deftly  swept 
over  the  plate  from  a  cup,  and  no  harm  will  be  done  with  the 
iron  developers  if  a  little  solution  should  run  over  the  edge  of 
the  plate.  The  iron  acts  more  rapidly  than  the  pyro  developer, 
and  the  latter  should  be  carefully  watched  and  instantly  rejected 
if  it  shows  signs  of  turbidity.  In  each  case  the  solution  is  to  be 
kept  moving  over  the  plate  until  the  image  has  gained  consid¬ 
erable  strength,  but  none  of  the  solutions  is  to  be  poured  on 
and  off  the  plate.  As  we  do  not  approve  of  re-development 
for  slide  making,  we  advise  that  the  developer  be  allowed  to 
act  fully,  provided  *no  muddiness  appears.  The  plate  is  now 


washed,  and  fixed  with 

0 

Potassic  cyanide .  20  grains 

Water . - . 1  ounce 

Or, 

Sodic  hyposulphite . 100  grains 

Water .  1  ounce 


We  prefer  the  cyanide,  but  it  is  a  dangerous  poison,  the 
handiest  antidote  in  case  of  accidental  imbibition  being  a  good 
draught  of  the  iron  developer.  After  fixing,  the  plate  is  to 
be  well  washed,  particularly  after  hypo. 

Frequently  the  slide  at  this  stage  wants  “  pluck.”  The  remedy 
is  intensification,  but  the  remedy  must  be  applied  with  caution. 


PRACTICAL  PHOTO-MICROGRAPHY. 


149 


Put  into  a  clean  cup  about  10  drops  of  a  solution  of  argentic 
nitrate,  bath  strength,  acidified  with  nitric  acid,  add  thereto 
about  4  drams  of  the  pyro,  or  iron  developer,  pour  this  on  the 
plate,  but  keep  it  moving,  and  beware  of  turbidity,  W ash  the 
plate. 

The  color  may  not  be  pleasing  at  this  stage,  in  which  case 
we  resort  to  toning.  Immerse  the  plate  in 


Platinic  chloride .  1  grain 

Nitric  acid .  1  minim 

Water . 3  ounces 


Watch  the  progress  and  remove  the  plate  when  the  color  is 
satisfactory.  A  fine  color  (engraving  black)  may  be  obtained 
by  toning  in  this  solution  till  the  image  is  bleached  and  almost 
disappears,  and  then  lightly  intensifying  with  iron  and  silver 
as  above. 

Mr.  Armstrong’s  Palladium  Toning  for  Slides. 


Palladic  Chloride .  15  grains 

Water .  15  ounces 

Nitric  acid . . . a  trace 


For  each  ounce  of  toner  take  1  dram  of  this  and  7  drams  of 
water.  Tone  till  the  color  penetrates  right  through  the  film, 
and  is  visible  from  back  of  the  plate. 

After  the  plate  is  dried  and  varnished  with  a  clear  varnish, 
(see  page  60)  it  is  cut  down  with  a  diamond  to  proper  size. 

rr 

Gelatine  Chloride  Plates  for  Slides. 

Print  in  contact.  As  even  with  gas  or  oil  light  the  exposure 
may  be  inconveniently  long,  a  good  plan  is  to  burn  a  measured 
length  (say  1  inch)  of  magnesium  ribbon  at  certain  distances, 
determined  by  trial,  from  the  frame.  For  a  beginning  the  inch 
of  ribbon  may  be  burned  at  10  inches  distance  for  a  moderately 
dense  negative.  The  exposure  to  diffused  daylight  may  be 
from  5  seconds  upwards.  If  magnesium  be  used  a  spirit-lamp 
may  be  utilized  to  ignite  the  ribbon,  a  spirit-lamp  would  require 
a  very  long  time  to  impress  the  plate. 

Development  is  performed  in  a  flat  dish,  the  plate  being 
placed  therein  face  upwards,  and  the  developer  poured  over 
the  plate. 


150 


PRACTICAL  PHOTO-MICROGRAPHY. 


Mr.  A.  Cowan’s  Formula  for  Development  of  G-elatine 

Chloride  Plates. 


a.  Ferrous  protosulphate . 140  grains 

Sulphuric  acid .  1  minim 

Water .  1  ounce 


Add  one  part  of  a  to  three  parts  of  one  of  the  following. 


For  Cold  Tones  after  Short  Exposure. 


b.  Potassic  citrate . 136  grains 

Potassic  oxalate .  44  grains 

Hot  water .  1  ounce 


For  Warm  Tones  after  Long  Exposure. 


c.  Citric  acid . 180  grains 

Ammonic  carbonate .  60  grains 

Water . 1  ounce 

Mr.  B.  J.  Edwards’  Formula. 

a.  Neutral  potassic  oxalate .  2  ounces 

Ammonic  chloride .  40  grains 

Distilled  water .  20  ounces 

b.  Ferrous  protosulphate .  4  drams 

Citric  acid .  2  drams 

Potash  alum .  2  drams 

Water  distilled . 20  ounces 


For  developing  mix  a  and  b  in  equal  parts. 

The  developer  is  allowed  to  act  until  the  image  is  seen 
plucky  in  every  part,  the  plate  is  then  well  washed  and  fixed 
in  “hypo,”  of  usual  strength.  If  any  scum,  due  to  salts  in 
the  water,  is  found,  it  may  be  removed  by  the  acid-alum  solu¬ 
tion  given  on  page  63,  the  solution  being  poured  on  to  the  plate. 

Beautifully  clear  slides  ought  to  result  from  this  treatment 
of  gelatine  chloride  plates.  These  plates  may  be  made  much 
more  sensitive  than  those  usually  sold,  but,  as  a  rule,  the  more 
sensitive  plates  are  inferior  in  quality. 

In  developing  these  plates,  it  is  well  to  develop  to  full  den¬ 
sity  at  least,  rather  beyond  than  short  of  it.  It  is  easy  and 
often  advantageous  to  reduce  the  slides'  after  fixation  thus : 


(Mr.  Cowan.) 

“  Strong  solution  of  iron  perchloride .  34  ounce 

Hydrochloric  acid .  24  ounce 

Water . 20  ounces 


PRACTICAL  PHOTO-MICROGRAPHY. 


151 


“Followed  after  washing  by  fresh  solution  of  hypo.” — (See 
page  63.) 

Gelatine  Bromide  Plates  for  Slides. 

In  this  process  we  have  certainly  the  quickest  method  of 
making  slides  for  the  lantern,  but  it  can  only  be  called  the  best 
method  when  worked  with  care  and  skill.  If  the  Reader 
proposes  to  make  all  his  lantern-slides  “  by  contact,”  he  had 
probably  better  use  chloride  plates ;  but  if  he  objects  to  the 
wet-plate  process,  he  will  find  the  process  we  now  describe  the 
best  for  his  purpose  if  he  has  to  reduce  or  copy  in  the  camera ; 
while  the  gelatine  bromide  process  may  be  made  to  answer 
admirably  for  contact  printing.  Ninety  per  cent,  of  the 
author’s  slides,  reduced  and  contact-printed,  are  made  with 
commercial  gelatine-bromide  plates. 

The  exposure  required  in  the  camera  is  from  three  to  ten 
times  less  than  with  wet  collodion,  the  difference  of  ratios 
depending  upon  the  sensitiveness  of  the  gelatine  plates  and 
the  quality  spectroscopically  of  the  light.  In  a  very  “  actinic” 
light  the  difference  is  minimized,  in  a  “  poor  ”  light  as  regards 
blue  and  violet  rays  the  gelatine  has  a  greater  “  pull.”  The 
bromide  plates  are  many  times  more  rapid  than  the  chloride 
plates,  not  less,  perhaps,  than  20  times. 

Exposure  is  made  in  the  usual  way,  but  the  light  of  the 
“  dark-room  ”  must  be  much  more  subdued  or  non-actinic  than 
for  collodion  or  chloride  plates.  This  fact  is  too  often  disre¬ 
garded. 

The  developers  we  recommend  are  ferrous  oxalate  and 
hydroquinone,  but  alkaline  pyro  is  also  available. 

The  ferrous  oxalate  developer  may  consist  of  one  part  of  the 
.saturated  ferrous  sulphate  solution  (page  63),  to  four,  five, 
or  six  parts  of  the  potassic  oxalate  solution  on  the  same  page. 
We  always  add  half  a  grain  of  soluble  bromide  to  each  ounce 
of  the  mixed  developer.  When  this  developer  is  applied  the 
image  should  begin  to  appear  after  about  thirty  seconds,  not 
before  twenty  seconds ;  density  and  detail  should  increase 
steadily  up  to  about  four  minutes  ;  when  the  development  is 
complete  the  image  seen  by  transmitted  light  ought  to  be 


152 


PRACTICAL  PHOTCBMICROGRAPHY. 


denser  than  appears  necessary,  for  the  fixing  makes  a  great 
difference.  "When  the  plate  is  watched  by  reflected  light  there 
should  be  no  sign  of  degradation  of  the  white  where  there  is 
no  image;  as  soon  as  any  such  “ graying ”  appears  the  plate 
must  be  swilled  with  water  containing  enough  acetic  acid  to 
make  it  smell  distinctly  of  that  acid,  the  developer  being,  of 
course,  poured  off,  either  down  the  sink  or  into  a  cup  for 
future  use.  The  developer  may  be  used  repeatedly  until  it 
either  turns  muddy  or  acts  too  feebly ;  each  time  it  is  used  it 
acts  with  less  vigor  than  previous  times,  on  account  of  fresh 
bromide  being  formed  and  on  account  of  oxidation. 

Unfortunately  it  is  sometimes  impossible  to  avoid  a  slight 
degradation  of  the  white  of  the  slide,  this  being  due  to  the 
want  of  density  of  the  negative  ground  in  comparison  with 
the  density  of  the  subject-image.  If  there  is  good  contrast 
of  density  between  subject  and  ground  there  ought  to  be  no 
sign  of  deposit  on  the  slide-ground,  and  any  such  deposit  is 
probably  due  to  overexposure  of  the  slide  plate  or  unsafe 
light.  A  very  slight  deposit  may  be  removed  by  the  acid  alum 
and  iron  solution,  used  after  fixation.  After  the  plate  has  been 
well  washed  in  the  acidulated  water,  three  changes  at  least,  it 
may  be  washed  under  the  tap  and  fixed  in  the  usual  hypo-bath. 
Thereafter  it  is  to  be  well  washed  and  then  the  following 
poured  on  and  off  from  a  height,  in  order  to  clear  any  deposit 
that  may  be  on  the  plate,  due  to  lime  salts. 


Saturated  Solution  of  Ferrous  Sulphate . 4  ounces. 

Saturated  Solution  of  Alum . 16 

Hydrochloric  Acid . . .  1  to  2  drams. 


The  IIydroquinonb  Developer.  (Mr.  Edwards.) 
Mix  in  the  following  order: — 


Sodic  Sulphite, .  2  ounces. 

Water . 20  “ 

Hydroquinone . 30  grains. 

Sodic  Carbonate.... .  3  ounces. 

Potassic  Carbonate .  3  “ 

Potassic  Bromide. . 40  grains. 


This  solution  will  not  keep  good  for  very  long,  but  if  the 
water  be  divided  into  two  parts  and  the  carbonates  separated 


No.  1.— Bacilli  Tuberculosis  in  Lung  of  Horse,  X  750. 


No.  2.— B.  Tuberculosis  by  Inoculation,  Lung  of  Rabbit,  X  600. 


Plate  VI. 


PRACTICAL  PHOTO-MICROGRAPHY. 


153 


from  the  hydroquinone,  the  two  solutions  will  keep  for  a  long 
time,  and  may  be  mixed  at  time  of  need. 

This  developer  acts  very  steadily;  if  exposure  has  been 
sufficient  failure  can  hardly  occur  with  suitable  negatives  and 
good  plates,  for  the  developing  action  only  requires  to  be 
watched  and  stopped  at  the  proper  time.  Fixing,  washing, 
and  clearing  may  be  conducted  as  usual.  This  developer  is 
strongly  recommended  for  Bromide  prints. 

Alkaline  Pyro  Developer. 

This  is  not  recommended  for  our  purpose  unless  there  be 
some  special  desire  for  warm  tones.  Sodic  Sulphite  as  a  pyro 
preservative  is  to  be  avoided  and  preference  given  to  potassic 
meta-bisulphite  see  page  61.  An  ounce  of  developer  may 


be  made  to  contain : 

Pyro . 1  to  grain. 

Potassic  Meta-bisulphite . 2  to  3  grains. 

Liquor  Ammonia,  880 .  . .  .2  minims. 

Potassic  or  Ammonic  Bromide . 2  grains. 

Water . to  1  ounce. 


The  rationale  of  developers,  of  which  the  above  may  be 
called  illustrative,  is  simply  a  well  restrained  development,  the 
potassic  salt  tending  to  produce  a  warm  tone,  coupled  with  full 
exposure  and  “  willing  ”  development. 

Here  again  fixing  and  washing  are  as  usual,  except  that  after 
fixation  if  a  warm  tone  be  desired  and  not  previously  obtained, 
the  washing  should  be  little  more  than  a  rinse,  and  the  acid- 
iron-alum  solution  applied  as  before  will  greatly  redden  the 
color  of  the  image  while  clearing  the  high  lights. 

All  lantern  slides  should  be  varnished  with  a  clear  varnish, 
usually  certain  colorless  gums  dissolved  in  benzole. 

To  mount  a  lantern  slide.  Clean  a  thin,  flawless  glass  plate 
3^  inches  square ;  select  and  lay  in  position  upon  the  face  of 
the  slide  a  suitable  mask  ;  on  the  mask  lay  the  cleaned  cover- 
glass.  Wet  a  gummed  “  strip,”  which  ought  to  be  about  fths 
of  an  inch  wide  and  14  inches  long  ;  lay  one  side  of  the  now- 
protected  slide  in  the  middle  and  at  one  end  of  the  wetted 
strip ;  turn  the  slide  over  side  by  side,  always  lifting  with  it 


154 


PRACTICAL  PHOTO-MICROGRAPHY. 


the  sticky  strip  and  always  turning  in  the  corners  of  the  strip 
and  running  the  fingers  along  back  and  front  of  the  slide  to 
make  the  strip  adhere  all  along.  On  reaching  the  last  corner, 
cut  or  tear  off  the  extra  bit  of  strip,  and  see  that  the  strip 
adheres  all  along  its  length  to  the  glasses.  Lay  the  slide 
down  face  up  as  it  is  wished  to  appear  on  the  screen,  and  then 
attach  two  white  marks  one  at  each  top  corner ;  these  marks 
for  a  guide  to  the  lanternist. 

Transferotype  prints  when  stripped  on  plain  glass  make 
fine  slides  ;  a  strong  point  being  that  they  may  first  be  dried 
and  then  trimmed  with  scissors.  They  are  then  well  soaked 
in  water  and  stripped,  see  page  128. 


CHAPTER  XXIII. 


USE  OF  THE  OPTICAL  LANTERN. 

Many  lecturers  and  teachers  are  quite  awake  to  the  advan¬ 
tages  that  would  arise  from  the  use  in  lecture  and  class-rooms 
of  the  optical  lantern,  but  almost  all  are  deterred  from  the  use 
of  this  valuable  instrument  by  a  mistaken  idea  as  to  the  diffi¬ 
culties  attending  its  use.  The  writer  has  conversed  on  this 
subject  with  several  Professors  of  note,  and  in  every  case  the 
difficulties  were  either  imaginary  or  exaggerated. 

It  is  admitted  that  under  certain  conditions  the  student  will 
learn  more  of  the  nature  of  his  subject  by  making  a  careful, 
even  if  faulty,  drawing  of  it  as  seen  in  the  microscope.  But 
in  very  many  cases  the  value  of  drawing  is  confined  to  the 
time  actually  employed  upon  the  sketch  ;  that  is  to  say,  that 
whatever  is  noticed  at  the  time  of  sketching  is  learned,  but 
nothing  more ;  and  the  sketch  thus  executed  can  never  teach 
anything  more.  A  photo-micrograph  not  only  reproduces 
details  independent  of  the  momentary  observation  of  the 
operator,  but  it  is  a  litera  scripta  which  is  itself  open  to  fur¬ 
ther  and  more  leisurely  and  careful  examination,  and,  more¬ 
over,  it  will  probably  contain  details  beyond  the  power  of  the 
hand  to  copy,  even  if  the  eye  noticed  them ;  and  if  there  is  one 
method  more  apt  than  another  to  lead  to  fresh  discoveries,  it  is 
the  method  of  enlarging  in  the  optical  lantern. 

So  much  for  the  student.  The  advantages  of  the  lantern 
will  be  even  more  sensible  to  the  teacher  than  the  taught. 
The  professor  presumably  knows  what  points  he  wishes  to 
demonstrate,  though  by  a  sketch  he  may  be  unable  to  dem¬ 
onstrate  them ;  and  every  one  knows  the  uncertainty  and  in-  » 
convenience  of  demonstration  to  a  class  by  one  or  more  micro¬ 
scopes  and  oral  explanations.  But  let  a  suitable  photograph 
be  produced,  a  lantern-slide  made  therefrom,  and  the  image 


156 


PRACTICAL  PHOTO-MICROGRAPHY. 


projected  upon  a  screen  in  front  of  the  class,  and  the  professor 
can  point  out  to  all  at  once,  without  a  possibility  of  mistake, 
the  appearances  and  the  parts  he  wishes  to  discuss.  Further, 
when  the  plioto-micrographic  negatives  are  to  be  used  for  this 
purpose,  the  necessary  magnification  is  so  greatly  reduced  in  all 
cases  that  the  original  operation  is  very  greatly  simplified,  and 
in  fact  the  results  are  probably  better  than  when  a  considerable 
original  amplification  is  necessary  in  order  that  the  points  may 
be  seen.  And  on  account  of  this  smaller  magnification  the 
surroundings  of  the  critical  object  are  better  rendered.  By 
the  process  we  now  discuss  the  teacher  shows  things  as,  and 
where,  they  are  ;  by  a  sketch  he  can  only  show  them  as  he 
thinks  they  are  or  ought  to  be. 


B»T£»t 


NEWTON  U  Co.  I  w 

DB  a  "•*■▼**  L AMO  ON  MSI 

■  K 

mm  j| 

II  1  P  ill 1  l  lli  I 

msm 

till 

Him  IB  [ 

■■■ii 

ii 

Fig.  36. — Lantern  Microscope. 


When  practicable  it  is,  perhaps,  better  to  show  the  object 
by  a  lantern  microscope,  or  by  a  special  arrangement  of  lantern 
and  the  essential  parts  of  a  microscope.  Here  is  figured  an 
arrangement  of  the  kind  alluded  to  (Fig.  36).  The  remarks 
of  this  chapter  will,  in  the  main,  apply  to  the  use  of  this  in- 
•  strument  as  well  as  to  the  use  of  an  ordinary  optical  lantern 
furnished  with  a  “photographic”  projection  lens,  and  used 
with  a  photographic  lantern  slide. 

But  it  is  easy  to  realize  that  the  use  of  the  lantern  microscope 


PRACTICAL  PHOTO-MICROGRAPHY. 


157 


is  limited,  because  the  number  of  subjects  suited  to  the  instru¬ 
ment  is  limited.  The  loss  of  light  in  projecting  a  large  image 
of  even  a  moderately  thick  object  is  so  considerable,  that  only 
in  exceptional  cases  can  success  be  expected.  Moreover,  as 
our  optical  science  now  stands,  the  combined  difficulties  of 
great  magnification,  illumination,  resolution,  and  definition  are 
too  great  to  be  satisfactorily  overcome,  except  in  specially 
favorable  circumstances.* 


Fig.  36  (a). 


The  instrument  known  as  an  optical  (or  vulgo  “magic”) 
lantern  is  quite  common  and  its  appearance  familiar  to  every 

*  Since  this  was  written  the  author  has  seen  a  greatly  improved  instru¬ 
ment  by  the  same  makers  and  for  the  same  purpose.  It  is,  however, 
costly.  It  is  shown  in  Fig.  36  in  its  latest  and  best  form. 


158 


PRACTICAL  PHOTO-MICROGRAPHY. 


one.  It  is  simply  a  box  to  hold  the  condenser,  object  or  slide, 
and  projecting  lens  in  certain  relations  to  each  other  and  to 
the  radiant,  and  to  prevent  the  radiant  from  illuminating  the 
screen  directly.  The  screen  is  usually  a  sheet  of  white  fabric, 
cloth  or  paper,  but  it  ought  to  be,  especially  for  purposes  now 
under  consideration,  an  opaque  white  surface,  as  plaster  on  a 
smooth  wall.  Paper  with  a  smooth  but  not  shiny  surface, 
pasted  to  a  wall  or  board  of  sufficient  size,  will  answer  every 
purpose.  The  diameter  of  the  screen  should  be  about  one- 
third  of  the  length  of  the  lecture  room ;  there  is  no  necessity 
for  much  more,  and  in  any  case  15  to  18  feet  will  be  the  extreme 
likely  in  ordinary  cases  to  be  convenient. 

An  oil  lamp  made  on  scientific  principles,  due  attention  to 
draught  being  the  main  feature,  will  illuminate  a  ten-feet 
screen  well,  an  eight-feet  one  perfectly.  Number  of  wicks *is 
of  less  consequence  than  the  position  of  the  wicks  with  relation 
to  each  other,  and  still  more  emphatically  with  relation  to  the 
condenser.  A  lantern  full  of  burning  wicks  will  give  less  light 
and  worse  confusion  than  one  wick  or  three  properly  placed. 
A  lantern  known  in  America  as  the  Scovill  “  Sciopticon  ”  is 
as  good  as  any  oil  lamp  we  know.  We  figure  this  article 
Fig.  36  (a). 

Perhaps  the  condenser  is  the  most  important  part  of  a  lan¬ 
tern.  It  should  be  a  double  one  certainly,  and  a  triple  is  by 
some  considered  superior.  A  condenser  which  works  very 
well  with  a  wick  lamp  need  not  be  the  best  for  the  lime-light, 
and  the  converse  holds  equally  good.  Still  a  condenser  which 
gives  an  even,  brilliant  image,  free  from  spherical  aberration, 
with  the  lime  light  will  suit  well  for  an  oil  lamp  with  one  or 
three  wicks  as  usually  arranged. 

Now  that  oxygen  is  obtained  in  our  countries  so  easily,  of 
so  good  quality  and  at  such  moderate  prices,  we  think  it  prob¬ 
able  that  a  lecturer  who  has  once  used  the  lime-light  would  not 
long  tolerate  the  nuisance  of  an  oil  lamp.  There  is  perhaps 
no  necessity  for  a  serious  nuisance  in  connection  with  oil ;  and 
whatever  trouble  there  is  will  fall  not  on  the  lecturer  so  much 
as  on  paid  assistants ;  none  the  less  the  inconveniences  of  lime- 


PRACTICAL  PHOTO-MICROGRAPHY. 


159 


light  are  so  small  compared  with  those  of  oil  that  we  recom¬ 
mend  the  former  in  all  cases  where  common  house  gas  is 
attainable.  For  any  ordinary  class  rooms  the  light  produced 
by  a  “  blow-through  ”  blow-pipe  on  a  “  soft  ”  lime  will  be  found 
ample,  either  for  projecting  a  photographic  slide  image  on  a 
12  to  15  feet  screen,  or  an  image  of  the  actual  object — if  suit¬ 
able  at  all — or  a  screen  of  about  5  or  6  feet  diameter,  using  in 
the  latter  case  a  microscopic  objective,  in  the  former  a  photo¬ 
graphic  lens  of  the  portrait  type.  For  our  “ blow-through” 
jet  we  require  one  tube  of  the  jet  to  be  connected  with  the 
gas  supply  of  the  building ;  the  oxygen  gas  we  keep  in  a  steel 
cylinder  under  pressure,  or  in  a  bag  between  weighted  pressure 
boards ;  these  with  a  supply  of  lime  cylinders  are  all  the  appli¬ 
ances  required.  There  is  no  smell,  no  cleaning  needed,  no 
danger,  nor  any  notable  heat.  There  are  several  forms  of 
blow-through,  or  as  it  is  sometimes  called,  “  safety  ”  jet.  The 
hydrogen  issues  and  burns  at  the  larger  orifice,  the  oxygen 
is  forced  at  some  pressure  through  the  hydrogen  flame, 
a  jet  of  the  two  gases  burning  impinges  on  the  lime,  which 
like  other  refractory  substances  gives  a  brilliant  light  in  com¬ 
bustion.  The  area  of  incandescence  with  this  jet  is  larger 
considerably  than  the  area  produced  by  the  “mixing-jet,” 
which  gives  a  light  both  smaller  and  brighter.  The  “  safety  ” 
jet  is  on  the  whole  better  adapted  for  the  lecture-room  than 
the  mixing  jet,  not  so  much  on  the  score  of  safety  as  on  that 
of  convenience.  A  mixing  jet  is  shown  in  Fig.  11. 

The  objection  usually  raised  in  our  hearing  to  the  use  of  the 
lantern  for  classes  is  the  difficulty  of  darkening  the  lecture- 
room*  There  need  be  no  trouble  on  this  point,  though  there 
may  be  some  expense  if  the  lectures  are  given  in  the  daytime. 
Ordinary  folding  shutters,  if  decently  fitted,  will  exclude  light 
sufficiently,  but  in  Britain  we  have  a  very  good  shutter  for  any 
purpose,  probably  the  best  for  all  purposes,  called  Clarke’s 
Patent  Shutter.  It  is  made  on  the  “  Louvre  ”  principle  of 
strips  of  metal  or  wood,  and  on  being  raised  it  coils  itself  up 
into  a  receptacle  above  the  window.  These  shutters  can  be 
pulled  in  a  few  seconds,  and  in  the  writer’s  house  they  shut 
out  every  beam  of  light  that  could  mar  the  lantern  image. 


160 


PRACTICAL  PHOTOMICROGRAPHY. 


The  axis  of  the  lantern  optical  system  may  be  horizontal, 
and  the  lantern  may  be  raised  so  that  this  axis  “  produced  ” 
falls  upon  the  centre  of  the  s  creen  ;  or  the  lantern  may  be 
placed  on  an  ordinary  table  or  stand  tilted  upwards ;  and  the 
screen  tilted  the  opposite  way  until  it  is  perpendicular  to  the 
optical  axis  of  the  lantern. 

The  lantern  slides  are  held  in  position  in  the  lantern  by  a 
device  known  as  a  “  carrier.”  The  simpler  this  carrier  is  the 
better,  provided  that  the  slides  can  be  easily  and  certainly 
centred.  No  carrier  for  our  purpose  is  likely  to  excel  the  old 
“Chadwick,”  well  known  in  England,  at  least;  but  one  of  the 
mechanically  centering  ones  may  be  used. 

The  projection  lens  should  have  a  focal  length  suitable  to 
the  size  of  disc  required  and  the  distance  from  lantern  to 
screen. 

S—  Size  of  opening  in  slide  in  inches. 

Z>=Diameter  of  disc  in  feet. 

Z=:Distance  of  lantern  from  screen  in  feet. 

Zh=Focal  length  of  projection  lens  in  inches. 

r  DXF  LXS  Lx  S 

z  =  ~  •  z  =  —  •  f=~d- 

(From  “The  Magic  Lantern  Manual,”  by  W.  I.  Chadwick. 
London  :  Warne  &  Co.) 

A  good  light  is  obtained  more  by  careful  adjustment  of  the 
proportions  of  the  gases  than  by  heavy  pressure.  It  is,  of 
course,  necessary  to  accurately  centre  the  various  parts  of  the 
optical  system,  and  to  get  the  radiant  as  nearly  as  may  be  in 
the  exact  focus  of  the  condenser. 

The  limes  should  be  always  kept  in  a  dry  or  air  tight 
receptacle,  and  it  is  well  to  heat  or  even  bake  them  for  a  short 
time  before  use. 

If  bag  and  pressure  boards  are  used  the  latter  must  have  a 
free  fall,  and  no  person  should  be  allowed  to  touch  the  bag 
when  the  gas  is  alight.  The  weights  must  be  of  such  shape, 
or  so  fixed,  as  to  have  no  chance  of  falling  off. 

If  any  hitch  should  occur  the  oxygen  is  to  be  turned  off 
first ;  on  lighting  up  at  first  the  hydrogen  is  always  to  be 


PRACTICAL  PHOTOMICROGRAPHY. 


161 


lighted  before  the  oxygen,  and  the  full  brilliance  is  to  be  got 
by  turning  on  the  gases  alternately  little  by  little.  The  “  cut 
off  ”  jet  designed  by  the  writer  is  specially  recommended  for 
the  lecture  room,  gas  and  trouble  $re  greatly  economized  by 
the  simple  contrivance  (see  page  44). 

Oxygen  and  hydrogen,  if  desired,  may  very  conveniently 
be  stored  in  gas  tanks  or  holders  made  of  sheet  iron.  The 
gases  may  be  used  directly  from  such  tanks.  If  bags  are  used 
for  the  two  gases,  each  bag  should  be  conspicuously  marked 
“H  ”  or  “  O,”  or  the  bags  should  be  different  in  appearance. 
There  is  no  necessity  for  an  accident  even  if  the  gases  should 
get  mixed  in  one  bag  provided  that  the  pressure  be  kept  up  ; 
but  risk,  however  slight,  should  be  avoided.  With  the  gas  in 
cylinders  there  is  no  risk. 

Postscript . — A  learned  professor  has  just  suggested  another 
difficulty  to  the  writer.  “  lrou  do  not,”  says  this  experienced 
teacher,  “  know  medical  students  in  the  dark !  ”  The  writer 
admits  his  inexperience,  but  would  gladly  run  the  risks  of 
gases  and  students  mixed. 


CHAPTER  XXIV. 


IMMERSION,  APOCHROMATICS,  AND  APERTURE. 

OCULARS. 

The  two  greatest  improvements  made  in  our  optical 
appliauces  within  a  period  of  many  years  have  been,  first,  the 
introduction  of  the  “homogeneous  immersion”  system  for 
objectives;  and  second,  the  use  of  a  new  glass,  having  different 
dispersive  powers  from  glasses  previously  made.  The  result 
of  the  discovery  of  this  new  glass  is  that  in  the  new 
apochromatic  objectives  we  have  a  more  complete  correction 
for  color  than  ever  we  had  before ;  that  is  to  say,  the  new 
lenses  are  corrected  not  only  for  two  spectrum  regions  as 
formerly,  but  also  for  a  third  region. 

The  system  of  immersion  is  now  so  much  a  matter  of  ancient 
history  that  we  need  only  point  out  the  advantages  now 
universally  admitted  to  arise  from  the  latter  development  of 
immersion,  viz  :  Homogeneous  or  oil-immersion.  Before  the 
days  of  oil-immersion  trouble  arose  from  the  fact  that  between 
the  object  and  the  objective  two  media  of  different  refractive 
powers  intervened,  viz  :  Crown-glass  (the  cover-glass)  and  air — 
or  water.  When  a  substance  was  found  having  approximately 
the  same  refractive  index  as  crown-glass,  and  when  the 
objective  was  practically  joined  to  the  cover-glass  by  this 
substance,  viz  :  an  oil,  it  is  easy  to  see  how  great  a  step  was 
gained,  provided  always  that  the  object  was  either  in 
contact  with  the  cover-glass,  or  in  a  medium  nearly  equal 
in  refractive  power,  and  in  contact  with  the  cover. 
More  oblique  rays  passed  from  object  to  objective,  the 
illumination  was  better,  working  distance  greater,  and  in  fact 
there  was  improvement  in  almost  every  respect.  By  the 
immersion  system  lenses  can  be  produced  of  larger  aperture 


PBACTICAL  PHOTOMICKOGKAPHY. 


163 


than  the  limit  available  with  dry  lenses,  and  the  “  fan  ”  of 
diffraction  rays  is  by  immersion  “  closed  up.” 

To  narrate  the  causes  and  considerations  that  led  to  the 
adoption  of  numerical  aperture  as  the  basis  of  calculation  of 
the  apertures  of  objectives  would  be  both  tedious  and  out  of 
place.  ¥e  content  ourselves,  therefore,  with  saying  that  to 
Professor  Abbe  is  due  the  system  of  calculation  now  almost 
universal,  and  by  permission  of  the  Royal  Microscopical 
Society,  we  give  in  the  latter  part  of  this  book  a  table  of 
apertures,  showing  the  relation  between  “  N.  A.”  and  angular 
aperture,  together  with  other  matter  of  great  value  to  the 
microscopist.  It  is  important  to  remember  that  resolution  is 
proportional  to  numerical  aperture  but  not  to  angular  aper¬ 
ture. 

The  maximum  air  angle  being  1,  we  have  oil  immersion 
lenses  with  numerical  aperture  as  high  as  1.5,  but  nothing 
above  1.43  has,  so  far  as  we  know,  been  made  practically  useful. 

The  immersion  system  is  also  used  for  condensers,  and 
theoretically  we  ought  to  be  able  to  use  the  whole  aperture  of 
the  highest  apertured  glasses,  but  few,  if  any,  glasses  are 
sufficiently  well  corrected  to  stand  utilization  of  their  entire 
aperture.  (See  paper  by  Mr.  E.  M.  Nelson  in  “English 
Mechanic,”  No.  1,234,  Nov.  1888,  for  information  on  this 
subject,)  Messrs.  Powell  and  Leland  make  a  fine  apochromatic 
condenser  N.  A.  1.4.  Zeiss  constructs  a  similar  article  N.  A.  1, 
while  many  opticians  make  non-achromatised  oil-immersion 
condensers  up  to  N.  A.  1.4,  or  nearly  so. 

Apochromatic  homogeneous  immersion  objectives  of  high  N. 
A.  are  at  present  the  acme  of  microscopical  practical  optics. 
But  while  resolving  power  increases  with  numerical  aperture 
the  quality  called  penetration  decreases  as  resolving  power 
increases.  We  have,  however,  tried  to  show  in  an  earlier 
chapter  that  this  “  penetration  ”  is  a  bogus  quality,  and,  in  fact, 
a  .defect  though  a  deceptive  one.  Nevertheless  there  are 
occasions  not  a  few  when  moderate  sharpness  on  various  planes 
is  preferable  to  absolute  sharpness  on  any  one  plane,  and  in 
such  cases  the  utilized  aperture  of  the  lens  may  be  easily  cut 
down  by  stopping  down  the  condenser  to  any  desired  extent 


164 


PRACTICAL  PHOTO-MICROGRAPHY. 


short  of  loss  of  definition  and  resolution.  Definition  and 
resolution  as  technical  terms  must  not  be  confounded.  Reso¬ 
lution  consists  in  visibly  separating  close  markings,  definition 
consists  in  imaging  distinctly  small  compact  objects. 

In  order  to  obtain  the  full  benefit  of  the  series  of  apocliro- 
matic  objectives  made  by  Zeiss  it  is  necessary  to  use  in 
combination  with  these  objectives  the  “compensating  eye¬ 
pieces”  made  to  go  with  them.  In  order  to  obviate  the 
necessity  for  an  ocular  being  specially  made  to  suit  each 
objective,  Abbe  and  Zeiss  have  been  bold  enough  to  deliberately 
introduce  in  certain  objectives  certain  aberrations  which  are 
corrected  by  the  oculars. 

For  the  projection  of  a  real  image,  such  as  in  photo¬ 
micrography  we  require,  free  from  aberrations,  and  visually 
and  chemically  correct,  Abbe  has  designed  and  Zeiss  makes  a 
series  of  “projection  oculars.”  These  are  the  oculars  to  which 
we  have  referred  as  being  the  best,  if  not  the  only  good, 
oculars  for  photo-micrography. 

In  both  the  compensating  and  projection  eye-pieces  Zeiss 
follows  the  commendable  system  of  marking  the  eye-pieces,  not 
by  arbitrary  and  meaningless  letters,  as  “  A,”  “  B,”  or  “  C,” 
but  with  a  number  indicating  the  amount  to  which  the  object¬ 
ive  image  is  magnified  by  the  ocular  ;  but  it  is  to  be  noted  in 
calculating  the  magnification  of  an  image  produced  by  these 
oculars,  that  the  figure  on  the  ocular  is  accurate  only  for  the 
precise  tube  length  for  which  the  ocular  is  designed.  The 
No.  4  ocular  is  intended  for  the  continental  tube  of  160  milli¬ 
meters  (about  7  inches);  and  at  160  mm.  behind  the  posterior 
conjugate  focus  of  the  objective,  the  objective-image  is  magnified" 
just  four  times  by  the  No.  4  ocular  ;  but  if  we  are  caused  to 
alter  the  tube-length  in  order  to  obtain  better  “  correction  for 
the  cover  glass,”  the  calculation  no  longer  can  be  taken  as. 
accurate,  as  far  as  regards  our  total  magnification. 

The  magnification  given  by  a  projection  ocular  and  objective 
combined  on  a  screen  at  a  known  distance  from  the  ocular 
may,  with  convenience,  but  only  in  one  case  with  absolute 
accuracy,  be  calculated  by  dividing  the  distance  in  mm.  from 
ocular  to  screen,  multiplied  by  the  number  on  the  ocular,  by 


PRACTICAL  PHOTOMICROGRAPHY. 


165 


the  focal  length  in  mm.  of  the  objective.  Example :  With  an 
objective  of  3  mm.  focus,  a  No.  3  projection  eye-piece  and  a 
screen  thirty  inches  from  the  shoulder  of  the  ocular,  we  get  a 
magnification  of  approximately  750  diameters,  30  inches  = 
eay,  750  millimeters. 

750  X  3  (ocular)  _  ^ 

3  (focus  of  lens) 

But  this  applies  with  only  moderate  accuracy  when  we  have, 
for  instance,  racked  our  tube  to  10£  inches  in  place  of  the  250 
mm.  (10  inches)  for  which  the  ocular  and  objective  are  in¬ 
tended.  If,  however,  our  tube  length  be  really  250  mm.  our 
magnification  may  be  taken  as  almost  exactly  750  diars.  in  the 
above  given  example,  at  least  the  writer  has  not  been  able  on 
experiment  to  verify  any  inaccuracy  in  the  figures  given. 

The  future  advance  in  photo-micrography— if  there  is  to  be 
any  advance  in  the  optical  line — will  depend  upon  apochro- 
matic  objectives  and  condensers,  and  the  use  of  wide  angles. 
It  is  vain  to  say  that  all  the  greatest  discoveries  have  been 
made  with  low-angled  glasses,  though  the  statement  may  be 
perfectly  true.  Had  higher  angled  glasses  been  used  the  dis¬ 
coveries  would  have  been  made  all  the  sooner,  and  our  high¬ 
angled  glasses  of  to-day  demonstrate  with  perfect  ease  even  in 
unskilled  hands  what  required  years  of  study  and  the  most 
skilled  microscopists  to  certify  in  by-gone  days.  And  further, 
the  science  of  practical  optics  was,  say  twenty  years  ago,  far 
behind  where  it  is  now,  and  the  opticians  of  these  days,  in 
achieving  high  angles,  probably  introduced  such  errors  of  cor¬ 
rection  as  made  the  glasses  practically  worthless.  So  the  ob¬ 
servers  did  well  to  use  well  corrected  low-angled  glasses 
rather  than  faulty  high-angled  ones,  and  their  discoveries 
were  made  with  low-angled  glasses,  faute  de  mieux.  The 
writer  is  in  the  constant  habit  of  examining  numbers  of 
objects  of  the  most  diverse  kinds,  he  has  at  command 
high-angled  and  low-angled  glasses,  yet  even  for  cursory 
examination  of  such  subjects  as  pathological,  physiological, 
bacteriological  and  diatomaceous  objects,  he  invariably  takes 
as  if  by  instinct  the  widest  angled  glass  he  can  find,  of  suitable 


166 


PRACTICAL  PHOTO-MICROGRAPHY. 


power.  For  photo-micrography,  as  a  matter  of  course,  he  uses 
apochromatics,  and  always  at  the  highest  angle  possible  con¬ 
sistent  with  contrast  between  “  tissue  ”  and  ground.  No  doubt 
the  old  experienced  microscopist,  accustomed  to  low-angled 
glasses,  will  be  sceptical,  and  may  even  at  first  believe  in  the 
inferiority  of  the  wide  angles,  especially  if  he  use  an  imperfect 
system  of  illumination,  but  we  have  firm  confidence  that  after 
a  fair  trial  and  a  little  perseverance  and  fight  with  prejudice, 
the  newer  glasses  will  prove  victorious,  even  in  the  eyes  of  our 
fathers  of  microscopy.  If,  in  any  branch,  “  want  of  penetra¬ 
tion  ”  can  be  disastrous,  surely  that  branch  is  the  photo-micro¬ 
graphic  ;  yet  of  all  the  conditions  under  which  we  insist  on  a 
wide-angle  apochromatic  objective,  photo-micrography  is  the 
chief. 


CHAPTER  XXY. 


CLASSIFICATION  OF  OBJECTS— HOW  TO 
TREAT  THEM. 

While  we  can  not  attempt  to  give  definite  rules  for  the  treat¬ 
ment,  microscopic  or  photographic,  of  every  object  or  class  of 
objects  that  may  come  under  the  notice  of  the  Photo-micro- 
grapher,  still  in  onr  somewhat  varied  experience  of  various 
classes  of  objects  we  hav.e  noticed  facts  and  formed  opinions 
which  may  be  of  service  to  our  Readers.  In  hope,  at  least, 
of  such  service  being  rendered  we  shall  set  down  a  few  points 
noted  in  our  actual  work. 

Insect  preparations  are  almost  always  exceedingly  difficult  to 
photograph  well.  In  the  first  place  if  the  insects  are  of  any  size 
and  are  mounted  in  cells  as  they  ought  to  be,  and  not  flattened 
by  pressure  as  they  sometimes  are,  we  have  to  deal  with  the 
optical  “  difficulty  ”  of  focusing  at  once  various  planes.  To 
meet  this  trouble  the  lowest  available  “power”  should  be 
used,  and  stretch  of  camera  substituted  for  eye-piecing  as  a 
means  of  getting  magnification,  and  even  this  does  not 
help  us  much.  Making  small  negative  images  and  enlarging 
them  will  probably  not  help  matters  in  the  least,  in  our 
experience  “  enlarging  ”  has  never  been  of  any  service  in 
overcoming  the  difficulty  to  which  we  allude.  In  our  own 
work  the  most  marked  successes  in  this  line  have  been  obtained 
by  the  use  of  an  apochromatic  lens  of  70  millimetres,  or 
about  3  inches  facal  length,  and  a  camera  stretch  of  from  5 
to  7^  feet.  The  illumination  in  a  case  such  as  this  is  apt  to  be 
a  puzzle,  but  the  best  plan  is  perhaps  one  suggested  to  the 
writer  by  Mr.  E.  M.  Nelson  ;  namely  :  to  use  as  condenser  the 
field-glass  of  a  good  “  A  ”  eye-piece,  placed  close  behind  the 
object,  (i.  e.  between  the  object  and  the  light),  the  convex  sur¬ 
face  of  the  field-glass  being  turned  towards  the  light.  Other 


168 


PRACTICAL  PHOTO-MICROGRAPHY. 


glasses  may  doubtless  be  used,  but  this  is  the  one  most  likely 
to  be  within  reach  of  every  microscopist. 

The  other  salient  difficulty  with  insects  is  a  photographic 
one  and  depends  on  color.  Insects  are  frequently  very  dense 
yellow  in  color  which  may  be  overcome  by  use  of  color-correct 
plates  with  or  without  yellow  illumination ;  but  when  in  addition 
to  a  densely  non-actinic  body  they  have  pellucid  wings,  antennae 
or  legs,  the  difficulty  becomes  very  great  indeed,  and  skilful  is 
he  who  can  surmount  such  a  concatenation  of  difficulties. 
Again  the  worker  must  look  to  careful  and  intelligent  use  of 
color-correct  plates  and  colored  screens  or  light.  Exposure 
must  be  full  for  the  densest  part  of  the  object ;  development 
should  be  sharp  and  short,  and  as  soon  as  details  are  out  in  the 
dense  parts,  the  negative  should  be  fixed  and  intensification 
resorted  to.  We  have  an  idea,  the  outcome  of  some  experi¬ 
ments,  that  for  this  class  of  work  the  hydroquinone  developer 
with  the  caustic  alkalies  soda  or  potash  is  eminently  suited. 
(See  page  96.) 

Pellucid  Objects ,  such  as  some  diatoms,  present  difficulties 
of  their  own  which  we  must  notice.  The  difficulty  is  partly 
in  the  optical,  partly  in  the  photographic  department  of  our 
work.  By  lowering  the  angular  aperture  of  our  lens  we  may 
produce  more  visual  contrast  between  the  pellucid  object  and 
the  ground  on  which  we  see  it,  but  we  at  once  lose  definition 
and  resolution.  This  holds  good  in  the  photographic  as  well 
as  ocular  branch.  If  we  lower  the  force  of  our  radiant-power 
we  improve  matters  visually  by  taxing  less  the  “  accommoda¬ 
ting”  power  of  our  eye,  but  the  same  step  has  no  advantage 
in  our  photography,  for  lowering  the  light  simply  entails  in¬ 
creased  exposure.  With  objects  of  this  pellucid  nature  our 
best  plan  is  to  cut  down  the  angle  of  our  condenser  as  much  as 
we  can  without  any  loss  of  definition  or  resolution,  (which  is 
equivalent  to  using  as  much  as  necessary  of  our  objective’s 
available  aperture  and  no  more),  keeping  the  exposure  as  short 
as  is  consistent  with  getting  a  black  negative  ground,  using  a 
thickly  coated  plate,  an  emulsion  replete  with  silver  haloid, 
and  a  slow  system  of  development,  preferably  perhaps  hydro¬ 
quinone  with  sodic  or  potassic  hydrate  (“caustic”  soda  or 


PRACTICAL  PHOTOMICROGRAPHY. 


169 


potash.)  And  though  as  a  rule  we  consider  intensification  of 
negatives  after  fixing,  by  mercury  or  otherwise,  an  operation 
little  commendable,  we  must  confess  that  for  this  particular 
class  of  object  it  has  frequently  proved  vastly  useful  to  us. 
A  fine  sample  of  this  class  of  subject  is  a  “  plate”  split  off, 
usually  by  accident  in  cleaning,  a  diatom. 

Physio-and  Pathological  Preparations  are  easy,  difficult,  or 
impossible  to  reproduce  well  according  to  their  cutting  and 
mounting.  Assuming  that  the  points  to  be  portrayed  by  pho¬ 
tography  are  well  seen  by  the  eye,  it  is  our  business  to  over¬ 
come  difficulties  of  staining  ;  but  difficulties  of  uneven  mount¬ 
ing,  bad  sectioning  and  the  like  are  beyond  our  control.  We 
would  protest  here  both  for  our  own  sake  and  for  the  sake  of 
pathological  and  physiological  science,  against  the  mania, 
apparently  spreading,  for  gossamer  sections.  Granted  that 
there  are  cases  where  no  instrument  we  have  can  cut  a  section 
too  thin,  it  is  none  the  less  true  that  those  cases  are  exceed¬ 
ingly  rare.  A  section  cut  to  show  the  more  minute  bacteria, 
or  for  histological  purposes  in  general,  can  perhaps  not  be 
too  thinly  cut,  but  for  ordinary  physiological  and  patho¬ 
logical  research,  sections  are  often  cut  too  thin  to  be  of  an}7 
real  use;  and  they  are  most  obnoxious  to  the  photo-microg- 
rapher.  On  the  other  hand  tissues  imperfectly  or  improperly 
prepared  for  cutting  cannot  be  cut  thin  enough  for  any  useful 
purpose,  and  the  mischief  of  thick  cutting  is  made  all  the 
more  apparent  when  staining  that  would  be  good  for  ordinary 
sections,  is  used  on  these  “  slabs  ”  of  tissue.* 

Given,  however,  a  good  section  of  the  class  of  subject  now 
under  notice,  we  ought  to  produce  by  photography  a  repre¬ 
sentation  far  beyond  the  best  that  manual  dexterity  can' 
accomplish.  The  question  resolves  itself  into  one  of  color- 
correct  photography  with  careful  and  skillful  correction  of 
the  objective  specially  if  the  work  be  histological.  If  “  cells  ” 
are  to  be  shown  in  the  characteristic  state  of  health  or  disease, 
the  optical  adjustment  of  all  apparatus  must  be  perfect. 
Epithelial  cells,  for  instance,  may  be  horribly  travestied  by 
improper  lens  correction  or  false  lighting.  The  lowest  power 
should  be  used  that  will  show  the  formation  required  to  be 

*  There  are  those  who  maintain,  with  some  reason,  that  a  section  can 
hardly  be  too  thin,  provided  it  is  sufficiently  stained. 


170 


PRACTICAL  PHOTO-MICKOGRAPHY. 


shown.  If  a  one  inch  o.  g.  has  sufficient  aperture  to  show 
muscle  striation,  it  is  folly  to  use  a  one-eighth  o.  g.;  if  magnifi¬ 
cation  alone  is  wanted,  in  such  a  case  we  should  decidedly 
recommend  camera  enlargement. 

Isolated  histological  subjects  are  sometimes  very  difficult, 
the  difficulties  coming  under  various  heads  already. touched  in 
this  chapter  or  about  to  be  touched.  We  allude  to  such  things 
as  epithelium  cells,  red  and  white  blood  corpuscles,  sperma¬ 
tozoa,  etc.,  spread  on  a  slide.  These  objects  do  not,  as  a  rule, 
take  kindly  to  stains,  and  they  are  not  only  more  or  less 
rounded  but  require  considerable  magnification  to  make  their 
morphology  visible.  Here  again  we  must  look  to  color-correct 
photography  to  give  us  contrast,  and  to  accurate  correction 
objectives,  both  for  the  actinic  focus,  and  by  careful  collar 
or  tube  adjustment.  We  usually  meet  the  pale  red  or  blue 
of  such  staining  by  the  yellow  screens  and  yellow-sensitive 
plates.  Slow  development  carefully  restrained  is  indicated, 
and  sometimes  intensification  necessitated.  As  a  sample  of 
this  class  we  may  cite  the  task  of  reproducing  ciliated  epithe¬ 
lium  cells,  to  show  which  well,  cilia,  nuclei,  and  protoplasm,  is 
not  easy. 

The  ease  or  difficulty  of  photographing  cover  glass  prepara¬ 
tions  of  bacteria  depends  chiefly  on  their  staining.  The  stains 
most  frequently  used  for  such  preparations  are  either  violet 
(gentian)  or  red  (fuchsine).  Few  things  are  more  difficult  to 
photograph  than  a  microbe  lightly  stained  with  gentian  violet, 
or  very  lightly  with  fuchsine.  If  the  stain  in  either  case  be 
pale,  the  only  hopeful  method,  is  to  use  yellow  screens  and 
color-correct  plates,  no  more  angle  than  necessary  being 
•  brought  into  play.  Some  organisms  badly  stained  with 
Bismarck  brown  have  completely  baffled  all  our  attempts  to 
photograph  them.  In  the  case  of  pale  pink  staining,  some¬ 
times  the  result  of  faded  or  abortive  fuchsine  or  eosine  stain¬ 
ing,  the  signal  green  glass  screen  has  more  than  once  helped 
us,  but  in  most  cases  the  yellow  screen,  theory  to  the  contrary, 
has  proved  more  useful.  If  organisms  are  well  stained,  the 
colors  vigorous,  the  ground  clear,  the  material  evenly  and 
thinly  spread,  the  difficulties  of  this  class  of  works  are  great 


PRACTICAL  PHOTOMICROGRAPHY. 


171 


only  because  of  the  magnification  required.  We  have  suc¬ 
ceeded  well  in  such  work  with  a  cheap  “  student’s  ”  oil 
immersion  one-twelfth  by  Swift,  and  also  with  a  similar  one- 
twentieth  by  Reichert,  using  no  ocular  in  either  case ;  it  is 
within  our  knowledge  that  glasses  by  Powell  and  Lealand 
(specially  a  twenty-fifth),  Beck,  and  Seibert  have  been  success¬ 
fully  used  in  this  manner  and  for  the  same  purpose.  The 
demonstration  by  photography  of  flagella,  with  which  some 
micro-organisms  are  endowed,  depends  upon  most  accurate 
correction  of  objective  coupled  with  suitable  mounting  and 
staining.  Though  many  of  these  organisms  are  flagellated,  it 
is  a  most  difficult  matter  to  keep  the  flagella  visible  in  mount¬ 
ing,  and  it  is  little  less  difficult  to  photograph  them  when 
visible. 

Test  diatoms  present  the  usual  microscopic  difficulties  with, 
generally,  a  photographic  one  “  thrown  in,”  viz.,  the  difficulty 
of  getting  contrast.  In  these  cases  angle  must  not  be  dis¬ 
pensed  with,  for  the  great  point  is  not  only  to  get  resolution, 
but  to  get  very  strong  and  distinct  resolution.  The  photo¬ 
graphic  difficulties  must  be  overcome  by  photographic  skill 
and  not  by  sacrifice  of  optical  excellence.  The  diatoms  should 
be  absolutely  in  contact  with  the  cover  glass,  to  determine 
which  Beck’s  “  Vertical  Illuminator  ”  is  invaluable,  and  the 
medium  in  which  the  objects  are  mounted  should  be  of  suit¬ 
able  refractivity. 

It  seems  to  be  the  fate  of  every  photo-micrographer  of  any 
ambition,  sooner  or  later,  to  attempt  to  photograph  “  amphi- 
pleura  pellucida  in  lines.”  The  first  thing  is  to  get  a  frustule 
as  coarsely  marked  as  possible,  but  withal  clean  and  flat, 
mounted  in  a  medium  of  high  refraction  index.  The  “  striae  ”* 
seem  usually  to  run  about  95,000  to  the  inch.  The  lines  can¬ 
not  with  any  angular  aperture  open  to  us  be  clearly  shown  by 
axial  illumination,  and  oblique  illumination  is  attained  by  put¬ 
ting  into  the  condenser  a  disc  with  a  slot  of  one  or  other  of 
the  following  shapes :  B  being  preferable  in  most  cases.  This 
slot  is  variable  in  breadth  and  length,  and  must  be  chosen  to 
give  the  best  result  by  experiment.  A  strong  light  should  be 
used,  as  lime  light,  for  under  the  best  conditions  of  illumination 


172 


PRACTICAL  PlH OTOMIC ROGRAPHY. 


the  exposure  will  be  protracted.  During  the  long  exposure 
there  is  great  risk  of  motion  of  the  apparatus  not  only  from 
tremor  of  the  apartment,  but  from  heat  of  the  radiant  affecting 
the  apparatus.  An  alum  trough  is  therefore  recommended  be¬ 
tween  light  and  condenser. 


Fig.  37. 


If  the  edge  of  a  lamp-flame  or  the  face  of  a  lime  cylinder  is 
used  as  the  illuminating  surface,  the  frustule  must  be  arranged 
vertically  on  the  stage,  and  the  slot  of  the  condenser  stop  is 
to  run  parallel  to  the  frustule.  The  directions  of  valve  and 
light  are  therefore  shown  thus :  Fig.  38,  while  in  the  field  of 


the  microscope  almost  the  whole  will  be  dark,  except  the 
frustule  itself,  until  the  high  power  o.  g.  is  brought  into  play. 


PRACTICAL  PHOTO-MICROGRAPHY. 


173 


The  successive  operations  towards  “  setting  up  ”  this  object 
may  be  thus  described.  A  suitable  frustule  is  chosen,  a  me¬ 
dium  power  objective  being  used  to  centre  the  object  and  the 
light,  and  to  focus  the  condenser  accurately  upon  the  object. 
The  slotted  stop  is  then  inserted  in  the  condenser,  and  the 
effect  examined  with  the  medium  power ;  little  else  beside  the 
frustule  should  be  illuminated.  Both  high-power  objective 
and  condenser  must  be  oil  immersions  and  of  the  best  quality. 

The  high-power  objective  is  now  put  into  place  and  action, 
and  the  most  accurate  correction  by  collar  or  tube  length  ob¬ 
tained  by  experiment.  The  condenser  will  almost  certainly 
require  re-focusing  after  the  high-power  glass  is  brought  into 
play.  With  perfection  of  apparatus  the  white  lines  ought  to 
appear  about  four  times  as  broad  as  the  black  ones  (Nelson). 

The  focusing  of  the  image  on  the  screen  is  with  ordinary 
achromatic  lenses  exceedingly  difficult,  with  apochromatics 
less  so.  No  pains  should  be  spared  to  get  a  correct  focus, 
and  after  it  is  got  the  whole  apparatus  should  be  allowed 
to  rest  for  ten  minutes  at  least,  the  light  at  full  blaze ;  after 
this  time  the  image  is  to  be  again  examined  to  test  for  steadi¬ 
ness.  Clearly  if  the  accuracy  is  lost  in  ten  minutes  it  is  hope¬ 
less  to  attempt  an  exposure  of  twenty  minutes  to  an  hour  with 
lime,  not  to  speak  of  four  to  ten  hours  with  an  oil  lamp.  We 
have  exposed  for  six  hours  on  this  diatom  with  oil,  and  our 
usual  time  with  lime  is  twenty-five  to  thirty  minutes ;  with 
these  exposures  we  expect  to  get  a  good  photographic  negative ; 
if  there  has  been  no  motion  of  the  image  we  are  much  pleased 
and  somewhat  surprised.  There  is  no  special  difficulty  in  de¬ 
velopment. 

In  spite  of  all  these  details,  A.  pellucida  is  child’s  play  to 
photograph  in  comparison  with  such  tests  as  P.  angulatum ,  8. 
gemma ,  and  N.  rhomboides  by  axial  light  and  to  show  “  black 
dots.”  P.  angulatum  in  white  areoles,  or  N.  rhomboides  in 
squares  with  a  special  disc  in  the  condenser,  is  infinitely  easier 
than  the  same  in  black  dots. 


CHAPTER  XXYI. 


BLACK  BACKGROUNDS.  OPAQUE  MOUNTS. 

POLARIZED  OBJECTS. 

Photography  of  certain  lustrous  objects  upon  a  dark  ground 
is  not  merely,  as  some  think,  a  playful  way  of  producing  a 
sensational  picture,  but  is  in  many  cases  a  really  useful  method 
of  depicting  suitable  objects.  We  have  seen  a  lecture  on 
Diatom  Structure  illustrated  almost  entirely  by  lantern-slides 
of  diatoms  on  black  ground ;  many  crystals,  and  certain  eyes 
are  better  seen  on  such  a  ground  than  on  a  white  one. 

When  objects  are  “mounted  opaque”  they  require  to  be 
photographed  by  reflected  light,  and  the  background  is  then 
naturally  dark,  but  when  objects  are  mounted  in  the  common 
way  on  clear  glass,  we  require  for  a  black  ground  one  or  other 
of  several  optical  instruments.  First  we  mention  a  “  spot  lens,” 
which,  before  it  became  obsolete,  was  used  below  the  stage, 
but  is  now  entirely  replaced  by  a  “  paraboloid,”  or,  better,  by 
the  addition  of  certain  disc-stops  to  an  ordinary  substage  con¬ 
denser.  The  paraboloid  is  a  very  pretty  piece  of  optical 
ingenuity,  sometimes  called  “parabolic  illuminator,”  but  in 
practice  the  condenser  with  stops  will  be  found  superior. 

For  this  class  of  work  the  achromatic  substage  condenser  is 
usually  furnished  with  a  set  of  the  discs  figured  No.  5,  and 
there  is  in  the  fittings  of  the  condenser  a  slot  or  other  recep¬ 
tacle  to  receive  the  stops.  With  powers  higher  than  a  quarter- 
inch  it  will  be  found  somewhat  difficult  to  work  the  system 
properly,  still  it  is  not  impossible  to  obtain  good  results  even 
with  immersion  glasses.  The  practice  is  somewhat  as  follows : 
The  condenser  is  centred,  the  condenser  and  objective  focused 
as  usual  on  the  object,  but  in  the  present  work  a  bull’s  eye 
may  without  detriment,  and  even  with  advantage,  be  used  to 


PRACTICAL  PHOTO-MICROGRAPHY. 


175 


parallelize  the  rays  on  the  back  of  the  condenser.  Now  one 
or  other  of  the  black  discs  is  placed  in  the  condenser,  which 
may  be  racked  up  and  down  so  that  the  best  image  of  the 
object  and  the  blackest  ground  possible  are  attained.  The 
point  of  chief  importance  is  to  get  the  margins  of  the  object 
perfectly  sharp  against  the  black  ground,  and  the  secret  of  suc¬ 
cess  is  to  use  the  smallest  disc  that  will  give  a  brilliantly-lighted 
object  with  an  absolutely  black  ground.  The  “  spot  lens  ”  may 
aptly  be  likened  to  the  above  arrangement  minus  the  power  of 
altering  the  size  of  the  spot,  and  the  parabolic  illuminator 
may  take  a  place  midway  between  the  two,  for  it  has  a  certain 
range  of  adaptation  in  virtue  of  a  small  movable  “spot” 
worked  from  its  lower  end.  We  need  hardly  say  that  in  this 
work  a  prolonged  exposure  is  required,  more  prolonged  than 
might  be  expected  by  the  beginner. 


Fig.  39. — Lieberkuhn. 
(Beck.) 


Fig.  40. — Wenham’s  Parabolic 
Illuminator. 


On  the  whole,  we  should  prefer  a  spot  lens  to  a  paraboloid, 
were  we  compelled  to  use  one  or  other. 

When  an  opaque  mount  has  to  be  photographed  we  should 
use  the  Lieberkuhn  (Fig.  39)  when  it  is  available.  With  the 
Lieberkuhn  the  light  passes  from  the  radiant  round  the  object 
to  the  Lieberkuhn  (which  is  fixed  to  the  objective)  and  thence 
reflected  back  upon  the  object,  which  is  thereby  illuminated 
evenly  from  all  sides.  This  necessitates  an  object  mounted  on 
a  black  disc  having  a  clear  space  all  round  it. 

As  the  province  of  the  Lieberkuhn  is  to  reflect  and  focus 
the  rays  upon  the  object,  it  will  be  easily  understood  that  the 
Lieberkuhn  has  to  be  made  to  correspond  with  a  lens  of  a  par- 


176 


PRACTICAL  PHOTO-MICROGRAPHY. 


ticular  focus,  so  that  in  practice  a  Lieberkuhn  is  required  for 
each  objective  used  with  it. 


Fig.  41. — Mount  for  Lieberkuhn. 


Failing  a  Lieberkuhn  for  opaque-mounted  objects,  we  may 
have  recourse  to  any  other  system  of  condensing  rays  of  light 
upon  our  object.  Thus  the  light  may  be  thrown  upon  the 


Fig.  42. — Side  Reflector.  (Swift.) 


object  through  a  bull’s  eye,  which  should  be  placed  at  an  angle 
as  narrow  as  possible  to  the  plane  of  the  object,  i.  e.,  as  near 
as  possible  to  the  microscope  tube. 


PRACTICAL  PHOTO-MICROGRAPHY. 


177 

Or  an  article  variously  known  as  a  “  parabolic  reflector,”  a 
“side  reflector,”  or  a  “cup,”  may  be  used  in  conjunction  with 
a  bull’s  eye.  The  action  of  the  cup  may  easily  be  gathered 
from  our  cut,  Fig.  42.  A  parallelizing  glass  will  be  useful 
here  also,  and  the  radiant  is  to  be  placed  on  a  line  perpendicu¬ 
lar  to  the  optic  axis  of  the  microscope. 

Polarising  apparatus  in  connection  with  photo-micrography  is 
often  of  great  value,  in  the  investigation  of  crystals  and 
crystalline  matters.  The  worker  in  this  line  must  be  prepared 
for  considerable  difficulties  in  color-rendering,  but  beautiful 
and  useful  results  have  been  achieved  by  some.  It  is  important 
to  use  prisms  as  large  as  possible,  to  consider  carefully  the 
selenite  to  be  used,  and  to  study  the  best  effects  in  color-rendering 
that  can  be  produced  by  modern  photography. 


Books,  etc.  Referred  to  or  Consulted 


Beale,  Dr.  Lionel  S.,  F.R.S.  “  How  to  Work  with  the  Microscope.” 

Harrison  :  London.  Lindsay  &  Blakiston  :  Philadelphia. 

Bousfield,  E.  C.,  L.R.C.P.  “Guide  to  Photo-Micrography.”  London: 
Kent  &  Co. 

Carpenter,  Dr.  W.  B.,  F.R.S.  “The  Microscope  and  its  Revelations.” 
London  :  Churchill. 

Crookshank,  Edgar  M.  M.B.  “Photography  of  Bacteria.”  London: 
H.  K.  Lewis. 

Jennings,  I.  H.  “Photo-Micrography.”  London:  Piper  &  Carter. 
Koch,  Dr.  R.  “  On  the  Investigation  of  Pathogenic  Organisms.” 
Translation  in  “  Microparasites  in  Disease,”  by  Victor  Horsley,  B.Sc., 
from  “  Mittheilungen  aus  dem  Kaiserlichen  Gesundheitsamte,”  Vol.  1. 
Berlin.  London  :  New  Sydenham  Society. 

Maddox,  R.  L.,  M.D.;  Hon.  F.R.M.S.  “Papers  in  British  Journal  of 
Photography ,”  passim,  and  elsewhere. 

Naegeli,  Prof.  Carl,  and  Schwendener,  Prof.  S.  “  The  Microscope 
in  Theory  and  Practice.”  London  :  Swan,  Sonnenschein  &  Co. 
Nelson,  Edward  M.  “  Papers  in  English  Mechanic,”  passim. 
Sternberg,  Miquel,  Truan,  De  Witt — and  others. 

Journal  of  Royal  Microscopical  Society,  passim,  London. 

Fraenkel  and  Pfeiffer.  “  Atlas  der  Bakterienkunde,"  Berlin,  1889. 
Abney,  Capt.  W.  de  W.,  R.E.,  F.R.S.  “Treatise  on  Photography.” 
London  :  Longmans,  Green  &  Co. 

Bothamley,  C.  H.  Papers  before  Photo  Convention,  1887,  1888,  1889, 
“  Journal  of  Chemical  Industry"  ;  also  “  Photo  News,"  passim. 

Burton,  Prof.  W.  K.  “  Practical  Guide  to  Photographic  Printing,”  etc. 
London  :  Marion  &  Co. 

Bur  i  on,  W.  K.,  and  Pringle,  Andrew.  “  Processes  of  Pure  Photog¬ 
raphy.”  New  York  :  The  Scovill  &  Adams  Co. 

Hardwich,  T.  F.,  and  Taylor,  J.  T.  “Photographic  Chemistry.” 
New  York  :  The  Scovill  &  Adams  Co. 


180 


PRACTICAL  PHOTO-MICROGRAPHY. 


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182 


PRACTICAL  PHOTO-MICROGRAPHY 


By  special  permission 


APERTURE  TABLE 

•mission  or  the  Royal  Microsc 


Royal  Microscopical  Society. 


Numerical  Aperture. 

(n  sin  u  —  a.) 

Corresponding  Angle  (2  u)  for 

Limit  of  Resolving  Power,  in 
Lines  to  an  Inch. 

Illuminating  Power. 

(a2-) 

Penetrating  /I  \  jj 

Power.  \a)  § 

§ 

■fe  L, 

^  ll 

S 

Water 

(n=  1-33). 

Homogeneous 

Immersion 

(n  =  1*58). 

4*  * 

rd  O 

fcuC  ZD 

wo® 

<©  o.2 

2  iH 
£  ^ 

Monochromatic 

(Blue)  Light. 

(A  =  0-4861  fi, 

Line  F. 

Photography. 

(A  =  O' 4000  n, 

near  Line  h). 

1  53 

180°  0' 

146,543 

158,845 

193,037 

2-310 

•658 

151 

166°  51' 

145,579 

157,800 

191,767 

2  280 

•662 

1  50 

161°  23' 

114.615 

156,755 

190,497 

2-250 

•667 

1  49 

•  • 

157°  12' 

143.651 

155,710 

189,227 

2  220 

•671 

1-48 

153°  39' 

142.687 

154,665 

187,957 

2-190 

•676 

1  47 

150°  32' 

141,723 

153,620 

186,687 

2  161 

•680 

1-46 

147°  42' 

140,759 

152,575 

185,417 

2-132 

•685 

1  45 

145°  6' 

139,795 

151,530 

184,147 

2  103 

•690' 

1-44 

142°  39' 

138,830 

150,485 

182,877 

2-074 

694 

1  43 

140°  22' 

137.866 

149.440 

181.607 

2015 

•699 

1  43 

138°  12' 

136,902 

148,395 

180,337 

2-016 

•704 

1  41 

136°  8' 

135,938 

147,350 

179,067 

1-988 

•709 

1  40 

134°  10' 

134,974 

146,305 

177,797 

1-960 

•714 

1*39 

,  , 

132°  16' 

134,010 

145,260 

176,527 

1-932 

•719 

1  38 

130°  26' 

133,046 

144,215 

175,257 

1904 

•725 

1  37 

128°  40' 

132,082 

143,170 

173,987 

1-877 

•739 

1-36 

126°  58' 

131,118 

142,125 

172,717 

1-850 

•735 

1-35 

125°  18' 

130,154 

141,080 

171,447 

1-823 

•746 

1-34 

123°  40' 

129,189 

140,035 

170,177 

1796 

-.741 

1  33 

180°  0' 

122°  6' 

128.225 

138,989 

168,907 

1-769 

•752 

1  33 

165°  56' 

120°  33' 

127.261 

137,944 

167,637 

1-742 

•758 

131 

160°  6' 

119°  3' 

126,297 

136,899 

166,367 

1-716 

•763 

1  30 

155°  38' 

117°  35' 

125,333 

135,854 

165,097 

1-690 

•769 

1  29 

151°  50' 

116°  8' 

124/.69 

134,809 

163,827 

1-664 

•775 

1-28 

148°  42' 

114°  44' 

123,405 

133,764 

162,557 

1-638 

•781 

1  27 

145°  27' 

113°  21' 

122,441 

132,719 

161,287 

1-613 

•787 

1  26 

142°  39' 

111°  59' 

121,477 

131,674 

160,017 

1-588 

•794 

1  25 

140°  3' 

110°  39' 

120,513 

130,629 

158,747 

1-563 

•800 

1  24 

137°  36' 

109°  20' 

119,548 

129,584 

157,477 

1-538 

•806 

1  23 

135°  17' 

108°  2' 

118,584 

128,539 

156,207 

1-513 

•813 

1  22 

133°  4' 

106°  45' 

117,620 

127,494 

154,937 

1-488 

•820 

1  21 

130°  57' 

105°  30' 

116,656 

126,419 

153,668 

T464 

•826 

1  20 

128°  55' 

104°  15' 

115,692 

125,404 

152,397 

1-440 

•833 

1  19 

126°  58' 

103°  2' 

114,728 

124,359 

151,128 

1-416 

•810 

1-18 

125°  3' 

101°  50' 

113,764 

123,314 

149,857 

1-392 

•847 

1  17 

123°  13' 

100°  38' 

112,799 

122,269 

148  588 

1369 

•855 

1  16 

121°  26' 

99°  29' 

111,835 

121,224 

147,317 

1-346 

•862 

1  15 

119°  41' 

98°  20' 

110,872 

120,179 

146.048 

1-323 

•870 

1  14 

118°  O' 

97°  11' 

109,907 

119,134 

144,777 

1  300 

•877 

1  13 

116°  20' 

96°  2' 

108.943 

118,089 

143,508 

1-277 

•885 

112 

114°  44' 

94°  55' 

107,979 

117,044 

142,237 

1-254 

•893 

111 

113°  9' 

93°  47' 

107,015 

115,999 

110,968 

1-232 

•901 

no 

111°  36' 

92°  43' 

106,051 

114,954 

139,698 

1-210 

■909 

1  09 

110°  5' 

91°  38' 

105,087 

113,909 

138,428 

1-188 

•917 

1  08 

108°  36' 

90°  31' 

104,123 

112,864 

137,158 

1-166 

•926 

1-07 

107°  8' 

89°  30' 

103,159 

111,819 

135,888 

1-145 

•935 

1  06 

105°  42' 

88°  27' 

102,195 

110,774 

134,618 

1124 

•943 

1  05 

104°  16' 

87°  24' 

101,231 

109,727 

133,348 

1-103 

•952 

104 

102°  53' 

86°  21' 

100.266 

108,684 

132,078 

1-082 

-962 

1  03 

101°  30' 

85°  19' 

99,302 

107,639 

130,808 

1-061 

■971 

1  02 

100°  10' 

84°  18' 

98,338 

106,593 

129,538 

1-040 

■980 

1-01 

98°  50' 

83°  17' 

97,374 

105,548 

128,268 

1-020 

•990 

1-00 

180°  O' 

97°  31' 

•  82°  17' 

96,410 

104.503 

126,998 

1-000 

1-000 

0  99 

163°  48' 

96°  12' 

81°  17' 

95,446 

103,458 

125,728 

•980 

1010 

O  98 

157°  2' 

94°  56' 

80°  17' 

94.482 

102,413 

124,458 

•960 

1020 

0-97 

151°  52' 

93°  40' 

79°  18' 

93,518 

101,368 

123,188 

•911 

1  031 

0-96 

147°  29' 

92°  24' 

78°  20' 

.92,554 

100,323 

121,918 

•922 

1042 

O  95 

143°  36' 

91°  10' 

77°  22' 

91,590 

99,278 

120,648 

•903 

1053 

©94 

140°  6' 

89°  56' 

76°  24' 

90,625 

98,233 

119,378 

"884 

1064 

O  93 

136°  52' 

88°  44' 

75°  27' 

89.661 

97,188 

118,108 

•865 

1-075 

092 

133°  51' 

87°  32' 

74°  30' 

88,697 

96,143 

116,838 

■846 

1-087 

0  91 

131°  0' 

86°  20' 

73°  33' 

87,733 

95,098 

115,568 

•828 

1099 

0  90 

128°  19' 

85°  10' 

72°  36' 

80,769 

94,053 

114.298 

•810 

1111 

089 

125°  45' 

84°  0' 

71°  40' 

85.805 

93,008 

113,028 

■792 

1124 

0-88 

123°  17' 

82°  51' 

70°  44' 

84.841 

91,963 

111,758 

•774 

1136 

PRACTICAL  PHOTO-MICROGRAPHY 


183 


APERTURE  TABLE.  — Continued. 


Numerical  Aperture. 

(n  sin  u  =  a). 

Corresponding  Angle  (2  u )  for 

Limit  of  Resolving  Power,  in 
Lines  to  an  Incb. 

Illuminating  Power 

(a  2). 

Penetrating  /1\  f 

Power,  f 

o' 

,b  ? 

s 

Water 

(n  =  1-33). 

Homogeneous 
Immersion 
( n  =  P52). 

White  Light 

(A  =  0-5269  ix. 

Line  E). 

Monochromatic 

(Blue)  Light 

(A  =  0-4861  ix, 

Line  F). 

Photography 

(A  -  0-4000  ix, 

near  Line  h). 

0  87 

120°  55' 

81°  42' 

69°  49' 

83,877 

90,918 

110,488 

•757 

1-149 

0  86 

118°  38' 

80°  34' 

68°  54' 

82,913 

89,873 

109,218 

•740 

1'163 

0  85 

116°  25' 

79°  37' 

68°  0' 

81,949 

88,828 

107,948 

723 

1-176 

6  84 

114°  17' 

78°  20' 

67°  6' 

80,984 

87,783 

106,678 

•706 

1-190 

0  83 

112°  12' 

77°  14' 

66°  12' 

80,020 

86,738 

105,408 

•689 

1-205 

0  83 

110°  10' 

76°  8' 

65°  18' 

79,058 

85,693 

104,138 

672 

1-220 

0  81 

108°  10' 

75°  3' 

64°  24' 

78,092 

84,648 

102,868 

•656 

1235 

0  80 

100°  16' 

73°  58' 

63°  31' 

77,128 

83,603 

101,598 

640 

1250 

0  79 

104°  22' 

72°  53' 

62°  38' 

76,164 

82,558 

100,328 

■624 

1266 

078 

102°  31' 

71°  49' 

61°  45' 

75,200 

81,513 

99,058 

•608 

1'282 

0  77 

100°  42' 

70°  45' 

60°  52' 

74,236 

80,468 

97,788 

•593 

1-299 

0  76 

98°  56' 

69°  42' 

60°  0' 

73,272 

79,423 

96,518 

‘578 

1316 

0  75 

97°  11' 

68°  40' 

59°  8' 

72,308 

78,378 

95,248 

•563 

1333 

0  74 

95°  28' 

67°  37' 

58°  16' 

71,343 

77,333 

93,979 

•548 

1351 

0  73 

93°  46' 

66°  34' 

57°  24' 

70,379 

76,288 

92,709 

533 

1370 

0  72 

92°  6' 

65°  32' 

56°  32' 

69,415 

75,242 

91,439 

■518 

1389 

0  71 

90°  28' 

64°  32' 

55°  41' 

68,451 

74,197 

90,169 

504 

1'408 

0  70 

88°  51' 

63°  31' 

54°  50' 

67,487 

73,152 

88,899 

•490 

1429 

0  69 

87°  16' 

62°  30' 

53°  59' 

66,523 

72,107 

87,629 

'476 

1'449 

0  68 

85°  41' 

61°  30' 

53°  9' 

65,559 

71,062 

86,359 

-462 

1471 

0  67 

&1°  8' 

60°  30' 

52°  18' 

64,595 

70,017 

85,0S9 

449 

1493 

0  66 

82°  36' 

59°  30' 

51°  28' 

63,631 

68,972 

83,819 

-436 

1515 

0  65 

81°  6' 

58°  30' 

50°  38' 

62,667 

67.927 

82,549 

'423 

1'538 

0  64 

79°  36' 

57°  31' 

49°  48' 

61,702 

66,882 

81,279 

•410 

1 '562 

0  63 

78°  6' 

56°  32' 

48°  58' 

60,738 

65,837 

80,009 

‘397 

1'587 

0  62 

76°  38' 

55°  34' 

48°  9' 

59,774 

64,792 

78,739 

'384 

1*613 

0  61 

75°  10' 

2 

O 

CO 

9 

47°  19' 

58,810 

63,747 

77,469 

'372 

1639 

0  60 

73°  44' 

53°  38' 

46°  30' 

57,846 

62,702 

76,199 

’360 

1'667 

0  59 

72°  18' 

52°  40' 

45°  40' 

56,881 

61,657 

74,929 

'348 

1695 

0  58 

70°  54' 

51°  42' 

44°  51' 

55,918 

60,612 

73,659 

’336 

1'724 

0  57 

69°  30' 

50°  45' 

44°  2' 

54,954 

59,567 

72,389 

'325 

1'754 

0  56 

68°  6' 

49°  48' 

43°  14' 

53,990 

58,522 

71,119 

'314 

1'786 

0  55 

66°  44' 

49°  51' 

42°  25' 

53,026 

57,477 

69,849 

303 

1'818 

0  54 

65°  22' 

47°  54' 

41°  37' 

52,061 

56,432 

68,579 

'292 

1 '852 

0  53 

64°  0' 

46°  58' 

40°  48' 

51,097 

55,387 

67,309 

'281 

1'887 

0  52 

62°  40' 

46°  2' 

40°  0' 

50,133 

54,342 

66,039 

'270 

1923 

0  51 

61°  20' 

45°  6' 

39°  12' 

49,169 

53,297 

64,769 

’260 

1-961 

0  50 

60°  0' 

44°  10' 

38°  24' 

48,205 

52,252 

63,499 

’250 

2 '000 

0  48 

57°  22' 

42°  18' 

36°  49' 

46,277 

50,162 

60,959 

'230 

2 '083 

0  46 

54°  47' 

40°  28' 

35°  15' 

44,349 

48,072 

58,419 

'212 

2' 174 

O  45 

53°  30' 

39°  33' 

34°  27' 

43,385 

47,026 

57,149 

'203 

2 ’222 

O  44 

52°  13' 

38°  38' 

33°  40' 

42,420 

45,981 

55,879 

'194 

2  273 

0  42 

49°  40' 

36°  49' 

32°  5' 

40,492 

43,891 

53,339 

'176 

2 '381 

0  40 

47°  9' 

35°  0' 

30°  31' 

38,564 

41,801 

50,799 

'160 

2 '500 

0  38 

44°  40' 

33°  12' 

28°  57' 

36,636 

39,711 

48,259 

'144 

2 '632 

0  36 

42°  12' 

31°  24' 

27°  24' 

34,708 

37,621 

45,719 

130 

2 '778 

0  35 

40°  58' 

30°  30' 

26°  38' 

33,744 

36,576 

44,449 

'123 

2 '857 

0  34 

39°  44' 

29°  37' 

25°  51' 

32,779 

35,531 

43,179 

'116 

2911 

0  32 

37°  20' 

27°  51' 

24°  18' 

30,851 

33,441 

40,639 

'102 

3 '125 

0  30 

34°  56' 

26°  4' 

22°  46' 

28,923 

31,351 

38,099 

'090 

3 ’333 

0-28 

32°  32' 

24°  18' 

21°  14' 

26,995 

29,261 

35,559 

'078 

3  571 

0  26 

30°  10' 

22°  33' 

19°  42' 

25,067 

27,171 

33,019 

'068 

3'846 

0  25 

28°  58' 

21°  40' 

18°  56' 

24,103 

26,126 

31,749 

063 

4 '000 

0  24 

27°  46' 

20°  48' 

18°  10' 

23,138 

25,081 

30,479 

'058 

4' 167 

0  22 

25°  26' 

19°  2' 

16°  33' 

21,210 

22,991 

27,940 

'048 

4 '545 

020 

23°  4' 

17°  18' 

15°  7' 

19.282 

20,901 

25,400 

'040 

5' 000 

0  18 

20°  44' 

15°  34' 

18°  36' 

17,354 

18,811 

22.860 

032 

5 '555 

0  16 

18°  24' 

13°  50' 

12°  5' 

15,426 

16,721 

20.320 

'026 

6 '250 

0.15 

17°  14' 

12°  58' 

11°  19' 

14,462 

15,676 

19,050 

'023 

6  667 

0  14 

16°  5' 

12°  6' 

10°  34' 

13,498 

14,630 

'  17,780 

'020 

7' 143 

012 

13°  47' 

10°  22' 

9°  4' 

11,570 

12,540 

15,240 

014 

8-333 

0.10 

11°  29' 

8°  38' 

7°  34' 

9,641 

10,450 

12,700 

010 

10  000 

0  08 

9°  11' 

6°  54' 

6°  3' 

7,713 

8,360 

10,160 

•006 

12-500 

0  06 

6°  53' 

5°  10' 

4°  32' 

5,785 

6.270 

7,620 

•004 

HV667 

0  05 

5°  44' 

4°  18' 

3°  46' 

4,821 

5,225 

6,350 

•003 

20  000 

INDEX. 


PAGE 


Abb6  on  N.  A .  163 

Abercrombie  and  Wilson,  Drs., 


Abnormal  Development .  97 

Actinism  .  42 

Adapter  with  Boyonet  Joint. . .  37 

Advances  of  Late,  Factors  in. .  67 

Advantages  of  Optical  Lan¬ 
tern .  155 

Advantages  of  Photo-micro¬ 
graphy .  15 

Aerial  Image,  Focusing  the.. . .  53 

Albumen  Paper,  Chemicals  for 

Printing  on .  59 

Albumen  Paper,  Manufacture 

of .  115 

Albumen  Paper,  Principles  of 

Use  of . 115 

Albumen  Paper,  Qualities  of . .  115 
Albumen  Paper,  Ready  Sensi¬ 
tized .  116 

Albumen  Paper,  “Salting”..  116 
Albumen  Paper,  Sensitising 

Bath  for .  64 

Albumen  Paper,  To  Sensitize  116 
Albumen  Prints,  Enamelling..  119 

Albumen  Prints,  To  Fix .  119 

Albumen  Prints,  To  Wash  ...  119 
Alkaline  Pyro  For  Gelatine 

Bromide  Slides .  153 

Alkaline  Solutions  for  Devel¬ 
opment .  62 

Alkaline  Toning  Solution....  118 

Alum  Acid  For  Clearing .  101 

Alum  Cell,  or  Trough .  54 

Alum  Solution .  63 

Ammonio-nitrate  for  Albumen 

Paper .  64 

Ammonio-sulphate  of  copper. .  42 

‘‘Amplifier,”  Not  Tried .  37 

Angular  Aperture  and  Reso¬ 
lution .  28 

Apartments  for  Work .  17 

Apartment  for  Work  to  be  Kept 

Dark .  78 

Aperture  and  Penetration .  30 

Aperture  and  Resolution .  163 

Aperture,, etc.,  Table,  (Royal 
Microscopical  Society).  .182,  183 

Aperture  of  Lenses . 162 

Aplanatic  Magnifier,  Zeiss....  53 


PAGE 


Apochromatic  Lenses .  162 

Apochromatic  Objectives,  Cor¬ 
rection .  28 

Apparatus  for  Enlarging .  135 

Apparatus  Used,  Vertical .  48 

Appearance  of  Plate  in  Devel¬ 
opment .  95 

Arachnoidiscus  Ehrenbergu,  to 

Photo .  81 

Archer .  12 

‘‘Area  of  Confusion” .  28 

Aristotype  Paper,  Operations. .  122 
Author’s  Complete  Apparatus.  50 
Author’s  Make-Shift  Illumin¬ 
ator .  71 

Aurantia  for  Colored  Screens.  108 

Azaline  Plates  For  Red .  107 

Bacteria,  Crookshank  on  Pho¬ 
tography  of .  13 

Bacteria  Preparations,  To 

Treat .  170 

Bags  For  Gases .  161 

Baker,  Mr.  C.,  his  Stand .  24 

Baker’s  “Nelson”  Lamp .  46 

Basement  cellar  for  Work .  17 

Beale,  Dr.  Lionel .  15 

Beck’s  Microscopes .  24 

Berkeley,  H.  B.,  his  Pyro- 

Formula .  61 

Black  Grounds .  174 

Black  Grounds,  Practice . 174 

Blistering  of  Gelatine  Plates..  103 
Blow-Fly’s  “Tongue,”  To  Pho¬ 
tograph .  84 

Blow-Through  Jet  For  Lantern  159 

Blow-through  Lime-jet  .  43 

Books,  etc.,  Consulted . 178 

Bothamley,  C.  H.,  Aurantia.  .  108 


Bousfield,  Dr.  E.  C.,  his  Book  14 

Box  For  Drying  Plates . 107 

Bromide  in  Developer,  Effect 


of .  ...  93 

Bromide  Paper .  123 

Bromide  Paper,  Chemicals  for 

Printing  on .  60 

Bromide  Paper,  Development 

of . 125 

Bromide  Paper,  Different 

Strengths  of  Developer .  126 

Bromide  Paper,  Exposure  Gen¬ 
erally  of .  125 


11 


INDEX. 


PAGE 


Bromide  Paper,  Exposure  of. .  123 

Bromide  Paper,  Fixing . 127 

Bromide  Paper,  Manipulation 

of .  12G 

Bromide  Paper,  Point  in  Favor 

of .  126 

Bromide  Paper,  Preparation  of  124 
Bromide  Paper,  Qualities  of.  .  125 

Bromide  Paper,  To  Glaze .  128 

Bromide  Paper,  To  Print  on..  125 
Bromide  Prints,  Permanence 

of .  129 

Bromide  Prints,  To  Expose  a 

Number  at  Once .  124 

Bromides,  Solutions  for  Devel¬ 
opment .  62 

Bull’s-eye  Described .  38 

Bull’s-eye,  How  to  Focus .  83 

Bull’s-eye,  How  to  Centre .  83 

Bull’s-eye,  Nelson  on  the .  82 

Bull’s-eye,  Term  Explained...  %% 

Bull’s-eye,  The  Effect  of .  “Si 

Bull’s-eye,  Use  and  Abuse  of  . .  69 

Bull’s-eye  Used  as  Condenser  .  70 

Burner  For  Developing  Room.  59 

Camera,  Maddox’s .  40 

Camera,  Stretch  of .  52 

Camera,  Woodward’s .  40 

Camera  for  Work .  50 

Camera  to  be  Blacked  Inside. .  77 

Campbell,  Fine  Adjustment..  26 
Camphor,  Added  to  Paraffine 

Oil .  45 

“  Canary  Medium  ” .  55 

Carbonates,  Solutions  for  De¬ 
velopment .  62 

Carbo’nates  for  Over-exposure  98 
Carbonic  Acid,  Restraining 

Power  of.. .  93 

Carburetted  Hydrogen  as  Radi¬ 
ant . 39 

Carpenter,  Dr. ,  his  Book .  30 

“Carriers”  or  “  Kits” .  52 

Castracane,  Count  Abbe .  15 

Caustic  Soda  or  Potash .  100 

Cell,  orTrough, For  Alum  Solu¬ 
tion .  54 

Centering  Bull’s-eye .  83 

Centering  the  Condenser .  81 

Centering  the  Light .  81 

Centre,  To  Mark  on  Ground- 

Glass  ....  .  80 

Chadwick  “Carrier”  For  Lan¬ 
tern  .  160 

Chemicals,  List  of .  59 

Chemicals,  Quantities  Required 

of . 7. .  60 


PAGE 


Citrates,  Solutions  for  Develop¬ 
ment .  62 

Citrates,  Use  of  as  Retarders  98 
Citrates  for  Over-exposure. ...  98 

Classification  of  Objects,  Treat¬ 
ment . 167 

Clearing  Solutions .  63 

Clearing  Solution  For  Gelatine 

Bromide  Slides .  152 

Clearing  the  Plates .  101 

Coating  Uneven  in  Plates....  104 
Cobalt  Blue  Glass,  Light-Filter 

(footnote) .  42 

Cold  Bath  Platinotype . .  133 

Collodion  as  Varnish .  103 

Collodion  versus  Gelatine 

Plates .  65 

Color-Correct  Photography. .. .  105 

Color  Correction  of  O.  G .  85 

Color  Sensitising  Bath,  Ery- 

throsin . 113 

Colored  Screens,  Howto  Use.  108 
Colors,  Effect  on  Exposure..  90 
Colors  Rendered  by  Photog¬ 
raphy .  105 

Compensating  Oculars .  164 

Condenser .  33 

Condenser,  Achromatic  Sub¬ 
stage .  33 

Condenser,  Achromatic,  by 

Powell  and  Leland .  .  . .  34 

Condenser,  How  to  Center  the.  81 
Condenser,  Nelson  on  the. . .  .  83 

Condenser,  Objective  Used  as.  73 

Condenser,  Oil-Immesion .  33 

Condenser,  Stops  for .  34 

Condenser,  Term  Explained..  22 

Condenser,  To  Focus  the .  81 

Condenser,  Use  and  Abuse  of.  69 

Condenser,  Uses  of .  34 

Condenser  for  Enlarging,  Area 

of .  139 

Condenser  for  Very  Low  Pow¬ 
ers  .  167 

Condensers,  Apochromatic,  by 

Various  Makers .  34 

Condensers,  Zeiss  Non-Achro- 

matic  .  33 

Confusion  in  Dark-room .  20 

Correction  of  Objectives  for 

Photography .  27 

“  Correcting  ”  the  Objective  by 

Color  or  Tube .  85 

Cover  Glasses,  Thick...*. .  31 

Critical  Image,  Conditions  for.  70 
Critical  Image,  Low  Power...  84 
Critical  Images,  Plates  for  ...  67 


INDEX. 


Ill 


PAGE 

Crookshank,  Dr.  E.  M .  13 

Crookshank  on  Photography 

of  Bacteria .  13 

Cup  Reflector .  177 

Cupric  Ammonio-sulphate _  42 

“Cut-off,”  Author’s  for  Lime- 

jet .  44 

Cyanin,  Sensitizer  to  Red  .....  lt>7 

Cylinders  For  Gases . . ...  161 

Dallinger  &  Drysdale,  Drs. ...  30 

Damp  in  Platinotype,  Precau¬ 
tions  Against .  131 

Dancer .  12 

Dark  Room  Window .  55 

Dark  Slide,  Mode  of  Fitting  to 

Camera .  52 

Darkening  Lantern  Lecture 

Room .  159 

Daylight  Enlarging .  135 

“  Deep”  Objects,  Photography 

of .  86 

Defects  in  Plates . 104 

‘  Definition  ”  Defined  .  164 

“  Depth  of  Focus”  .  28 

Details,  First  Appearance  of,  in 

Development .  94 

Developer,  Ferrous  Oxalate..  63 
Developer,  Ferrous  Oxalate 

Normal .  92 

Developer,  Pyro-ammonia. ...  91 

Developer,  Pyro-carbonate. . . .  91 

Developer,  Quantity  Required 

of .  98 

Developer,  Quinol  or  Hydro- 

quinone. . .  99 

Developers,  Normal... .  91 

Developing  Dishes .  57 

Developing  Plates,  Light  For..  55 
Development,  Abnormal ....: .  97 

Development,  Manipulations  of  92 
Development,  When  to  Stop..  95 
Development  of  Details,  Pro¬ 
gress  of .  93 

Development  of  Platinum  Prints  131 
Diaphragm,  Iris,  for  Condenser  34 

Diaphragms,  In  Ocular .  32 

Diaphragms  for  Condensers  .  34 

Diatoms,  Photos  of .  13 

Diatoms,  Test,  How  to  Treat. .  171 
Differential  Screw  Adjustment  24 

Diffraction-grating .  42 

Diffused  Daylight  as  Radiant..  42 

Disc  Size  For  Lantern .  158 

Dishes  For  Developing,  etc. . .  57 

Donne .  12 

Draper,  Dr.,  his  Work .  14 

Draw  Tubes,  Rack  Work  for. . .  24 


PAGE 


Drying  Box .  107 

Drying  Rack .  58 

Dusting  Plates .  104 

Easel  for  Enlargements . 140 

Eastman  Co.  Bromide  Paper.. .  127 
Eastman  Co.  Transferotype 

Paper .  127 

Eastman  Company’s  Easel  for 

Enlargement .  140 

“  Easy  ”  and  “  Difficult  ”  Work  20 
Easy  Objects  to  Photograph.  . .  79 

Echinus  Spine  as  a  Test .  32 

Edwards,  Mr.  B.  J.,  Isochro- 
matic  Plates,  Commercial...  106 
Effect  of  Condenser  On 

Illumination .  89 

Electric  Arc  Lamp .  43 

Electric  Incandescent  Lamp.  ..  43 

Electric  Light  as  Radiant .  39 

Electric  Light  as  Radiant .  43 

Enamelling  Albumen  Prints. . .  119 
Enlarged  Negative,  To  Pro¬ 
duce  .  141 

Enlarged  Versus  Direct  Nega¬ 
tives .  66 

Enlarging,  Condenser  for..  ..  139 

Enlarging,  Discussion  on .  134 

Enlarging,  Double  Camera  for.  136 
Enlarging,  Exposure  Required.  138 

Enlarging,  Lens  for . 136 

Enlarging,  Necessaries  for. . .  134 

Enlarging  by  Daylight .  135 

Enlarging  by  Optical  Lantern. .  138 
Enlarging  by  Optical  Lantern, 

the  Radiant .  139 

Enlarging  From  Gelatine  Nega¬ 
tives . 65 

Eosin,  For  Sensitizing  Plates.  .  106 
Erythrosin,  to  Use  For  Plates.  107 
Erythrosin  Bath,  Bothamley’s.  113 

Evans,  F.  H .  15 

Examples  of  Operations .  79 

Exposing  Shutter .  53 

Exposure .  88 

Exposure,  Duration  of .  39 

'  Exposure,  Greatly  Affected  by 

Color .  90 

Exposure,  Factors  Regulating  89 
Exposure,  Rapid,  How  to  Make  54 
Exposure,  Tables  Deprecated  88 
Exposure,  to  Judge  on  Devel¬ 
opment  .  98 

Exposure  Table,  Bousfield’s. .  89 

Eye-Piece  or  Ocular,  Use  of.  .  74 

Eye-Piecing,  Toleration  of. . . .  31 

Factors  Regulating  Exposure  89 
Farmer,  Howard,  his  Reducer  63 


IV 


INDEX. 


Ferrotype  Plates  for  Glazing 

Prints . 

Ferrous  Oxalate,  Normal  Devel¬ 
oper . 

Ferrous  Oxalate  Developer.. 
Ferrous  Sulphate  Solution.... 

Field,  Flatness  of . 

Field  Glass  of  Ocular  Used 

as  Condenser . 

Fine  Adjustment,  Differential 

Screw . 

Fine  Adjustment,  Long  Lever. . 

Fixing  Albumen  Prints . 

Fixing  the  Plates  . 

Fixing  Solution  for  Prints.... 
Flagella  of  Microbes,  To  Treat 

“Flares” . 

Flatness  of  Field . 

Flea,  Peculiar  Preparation  of.. 
Focal  Length  Regulates 

“  Power” . 

Foci,  Visual  and  Actinic  not  Co¬ 
incident  . 

Focusing  Bull’s-eye . 

Focusing  Condenser . 

Focusing  Eye-Piece . 

Focusing  Eye-Piece,  To  Set 

Focus  of . 

Focusing  Surfaces. . 

Focusing  the  Projection  Ocular 

Focusing  Various  Images . 

Fog,  To  Discover  Cause  of... . 

Fog  on  Negatives . 

Frsenkel  and  Pfeiffer,  Drs., 
their  Micrographs  of  Bacteria 

Frilling  of  Gelatine  Plates . 

Gas  Cylinders,  Safety  Of . 

Gas  Tanks . . . 

Gelatine  Bromide  For  Lantern 

Slides . . 

Gelatine  Bromide  Plates, Clear¬ 
ing . 

Gelatine  Bromide  Plates,  Fix¬ 
ing . 

Gelatine  Bromide  Slides,  De¬ 
velopers . 

Gelatine  Bromide  Slides,  Ex¬ 
posed . 

Gelatine  Chloride,  Characters 

of . 

Gelatine  Chloride,  Chemicals 

for  Printing  on . 

Gelatine  Chloride  Lantern 

Slides . 

Gelatine  Chloride  Printing. . . . 
Gelatine  Chloride  Slides,  Ex¬ 
posure . 


PAGE 

Gelatine  Chloride  Slides, 
Formulae  For  Developers...  150 
Gelatine  Chloride  Slides,  To 

Reduce  .  150 

Gentian  Violet,  To  Photograph  110 

Gibbes,  Heneage .  15 

Glass,  Cobalt  Blue  (foot  note).  4 2 
Glass  for  Collodion,  To  Clean.  147 

Glazing  Albumen  Prints . 119 

Gold  Chloride,  in  Tubes . 119 

Gold  Toning,  Rationale  and 

Use  of .  115 

Gold  Toning  Solution .  64 

Gotz,  Mr.  J.  R.,  Color-Sensitive 

Plates .  106 

Ground  Glass  of  Camera .  52 

Hartnack,  Student  Stands....  26 
Heliostat,  Generally  Required.  39 

High  and  Low  Angles .  165 

Histological  Subjects . 170 

History . 11-12 


Homogeneous  Immersion....  162 
“  Hook’s  Joint”  for  Focusing.  50 
Horizontal  Position  for  Stand..  22 
Hot  Bath  Process,  Platinotype.  131 

Hydrochinon  For  Slides . 152 

Hydroquinone  Developer .  99 

“  Hypo,”  Solution .  63 

Hypo,  To  Remove  from  Prints  119 

Illumination..., .  39 

Illumination  as  Affecting  Ex¬ 
posure .  89 

Immersion,  Advantages  of . . . .  162 
Immersion,  Homogeneous....  31 

Immersion,  System  Of . 162 

Immersion  for  Condensers..  163 
Incandescent  Lamp  as  Radiant  43 

Initial  Power .  75 

Insect  Preparations,  How  to 

Treat . 167 

Intensification  of  Gelatine 

Plates . 102 

Intensification  with  Mercury.  .  63 

Introduction .  ll 

Iron  Developer  for  Wet  Collo¬ 
dion  .  148 

Iron  Perchloride  for  Reducing  63 
Ives,  His  Orthochromatic  Pro¬ 
cess  .  107 

Jennings,  late  Isaac  H .  14 

jets  for  Lime  Light .  42 

Judgment  of  Exposure  in  De¬ 
velopment .  94 

Koch,  Dr.  R.,  his  Work .  13 

Lamp,  Microscopical .  22 

Lamps,  “  Non-Actinic  ” .  56 

Lantern,  Size  of  Disc .  158 


PAGE 

120 

92 

63 

63 

32 

167 

24 

26 

119 

101 

64 

171 

77 

32 

109 

31 

• 

27 

83 

81 

53 

53 

52 

85 

85 

104 

103 

16 

103 

161 

161 

151 

101 

101 

151 

151 

121 

60 

149 

121 

149 


INDEX. 


y 


Lantern  Microscopes,  Wright 

and  Newton’s . 

Lantern  Slides . 

Lantern  Slides,  Dry  Collodion. 
Lantern  Slides,  Gelatine  Bro¬ 
mide  . 

Lantern  Slides,  Gelatine  Chlo¬ 
ride  . 

Lantern  Slides,  Gelatine  Chlo¬ 
ride . . . 

Lantern  Slides,  Qualities  of. .  . 

Lantern  Slides,  Size  of . 

Lantern  Slides,  Various  Pro¬ 
cesses  for . 

Lantern  Slides,  Wet  Process  . . 

Lantern  Slides  by  Transfer . 

Lantern  Slides  on  Gelatine 

Bromide . 

Lantern  Slides  to  be  Varnished 
Lens,  Supplementary  for  “  Cor¬ 
rection  ” .  . 

Lens  for  Reduced  Slides . 

Lieberkuhn . 

Lieberkuhn,  Mount  for . 

Liesegang’s  Chloride  Paper... 

Light,  Lime . 

Light,  Monochromatic . 

Light,  To  Centre  the . 

Light  for  Operating  Room, 

Rationale  of . 

“  Light  Modifiers” . 

Lighting,  Even . 

Lighting  Uneven  on  Negative. 

Lime  Light . 

Lime  Light,  Author’s  Jet . 

Lime  Light,  Jets  Described... 

Lime-Light  as  Radiant . 

Limes  For  Lantern,  To  Pre¬ 
serve . 

Liquor  Ammonia,  To  Use.. 

Long  Lever  A  djustment  . 

Low  Power  Work,  “Portrait” 

Plates  for . 

Machines  for  Washing  Prints. . 

Maddox,  Dr.  R.  L . 

Maddox’s  Camera  Described. . 
Magnesia,  To  Replace  Limes. 

Magnesium  Ribbon  Light . 

Magnification,  Amount  of . 

Magnification,  as  Touching 

Exposure . 

Magnification,  To  Calculate. . 
Manipulation  of  Bromide  Paper 
Manipulations  of  Development 
Marking  Oculars.  Zeiss’  System 

Mercer,  Dr.,  his  Work . 

Mercury,  Intensifier . 


PAGE 

Methyl  Blue,  To  Photograph . .  110 


Microscope,  Baker’s  “  Nelson  ”  24 
Microscope,  Powell  and  Le- 

land’s .  24 

Microscope,  Swift’s  Wales  pat¬ 
tern  .  24 

Microscope,  The .  23 

“Microscope  and  its  Revela¬ 
tions,”  The,  by  Dr.  Carpenter  30 
Microscope  Attachment  to  Lan¬ 
tern .  156 

Microscopes,  Beck’s .  24 

Microscopes,  “Student’s”....  26 

Miguel,  Dr .  15 

Mis-focusing  Condenser,  Dan¬ 
ger  of .  72 

Mixing  Jet  For  Lantern .  159 

Mixing  Lime-jet .  43 

Monochromatic  Light .  42 

Mount  for  Lieberkuhn .  176 

Mounting  Glazed  Prints. . ....  .  120 

Mounting  Lantern  Slides .  153 

N.  Rhomboides .  173 

Negative,  A  Good  One  De¬ 
scribed . 103 

Negative  Varnish .  103 

Negatives,  Qualities  of .  103 

Negatives,  To  Print  Hard  and 

Soft .  116 

Negatives,  To  Reduce  Density 

Of .  102 

Nelson,  E.  M.,  his  Arrange¬ 
ments .  17 

Nelson,  E.  M.,  his  Work .  14 

Nelson,  Pattern  of  Micro  Stand  24 
Newton  &  Co.,  Jet  for  Lime 

Light .  44 

Neyt .  15) 

Non- A  chromatic  Condenser. . .  33! 

Normal  Developers .  6L 

Normal  Developers .  91' 

Nose-Pieces .  36 

Numerical  Aperture .  163 

Obernetter,  Color  -  Sensitive 

Plates .  107 

Objects,  Deep  ” .  86 

Objects,  Divided  Into  Classes  66 
Objective,  or  Object  Glass. ...  27 

Objective  Used  as  Condenser.  73 
Objectives,  Correction  of.  ...  27 

Objectives,  Testing .  31 

Ocular,  Convenience  of .  75 

Ocular,  Use  of .  74 

Ocular  or  Eye-Piece,  Stops  in.  32 

Oculars,  In  General .  37 

Oculars,  Projection  by  Zeiss..  164 


PAGE 

156 

143 

145 

145 

145 

149 

143 

145 

144 

144 

128 

151 

153 

27 

146 

175 

176 

121 

43 

40 

81 

56 

35 

49 

104 

43 

43 

43 

39 

161 

62 

26 

67 

119 

12 

40 

44 

124 

75 

89 

164 

126 

92 

164 

13 

63 


VI 


INDEX. 


PAGE 


Oculars,  Prbjection  Recom¬ 
mended .  37 

Oculars,  Zeiss  Compensating.  164 
Oculars,  Zeiss’  System  of  Mark¬ 
ing . 164 

Oil  Lamp  as  Radiant .  39 

Oil  Lamps  for  Microscope  ...  45 

Opal  Prints  by  Transfer .  128 

Opaque  Mounts .  174 

Operating  Room .  55 

Operating  Room,  Furniture 

For .  57 

Operating  Room,  Window  or 

Lamp  for .  55 

Operating  Room  Lamps .  56 

Operations  Following  Devel¬ 
opment . .  ....  101 

Optical  Lantern,  An  Objection 

To .  161 

Optical  Lantern,  for  Enlarging.  138 

Optical  Lantern,  Gas  For . 159 

Optical  Lantern,  Jets  For . 159 

Optical  Lantern,  Oil  Lamp. . . .  158 
Optical  Lantern,  Plea  For  Use 

Of .  155 

Optical  Lantern,  Table  of  Dis¬ 
tances,  Foci,  Disc, Sizes,  etc.  160 
Optical  Lantern,  To  Get  Good 

Light . 160 

Optical  Lantern  *•  Carriers”. . .  160 
Optical  Lantern  to  Darken 

Room .  159 

Orthochromatic  or  Color-Cor¬ 
rect  plates,  Light  For  Devel¬ 
oping . 55 

Orthochromatic  Photography. .  105 
Orthochromatic  Photography, 

Late  Advances  in . .  67 

Orthochromatic  Work,  Samples 

of . : .  109 

Orthochromatics .  21 

Orthochromatics, LateAdvances 

in .  106 

Orthochromatics,  Rationale  of.  105 
Orthochromatics,  Value  of....  106 

Orthochromatising  Plates .  107 

Over-exposure,  to  Remedy _  97 

Oxygen  Gas  For  Lantern . 158 

Oxy-hydrogen  Lime  Light .  43 

P.  Angulatum .  173 

P.  Angulatum ,  Photo’d  by 

Maddox . : .  13 

Paper  Albumenized,  Printing 


Parabolic  Illuminator . 174 

“Paraboloid” .  174 

Pellucid  Objects.  How  to  Treat  168 


FAGS 


Pellucida,  A,  “  in  lines” . 171 

Penetration,  Aperture,  Magnifi¬ 
cation .  30 

Penetration.  Defined .  28 

Penetration  and  Aperture .  29 

Penetration  in  Relation  to 

Aperture .  163 

Permanence  of  Bromide  Prints  129 
Perspective,  in  a  Diffraction 

Image .  30 

Photographic  Requisites .  55 

Photography,  Color-Correct. .  105 

Photography,  Orthochromatic..  105 

Photography,  Value  of .  11 

Photography  in  General,  to  be 

Studied .  21 

Photo-micrographers,  Classes 

of .  12 

Photo-micrography,  Claims  for  15 

Pigott,  Dr.  Royston .  30 

“Pinholes”  in  Plates .  104 

Pizzighelli’s  Platinum  Printing 

Process .  132 

Physio  and  Patho.  Prepara¬ 
tions,  How  to  Treat .  169 

Plane  Mirror,  Use  of,  With 

Daylight .  42 

Plate  Glass  to  Focus  on .  53 

Plates,  Common  Sizes  of .  52 

Plates,  List  of  for  Stock .  68 

Plates,  Selection  of .  65 

Plates,  to  Orthochromatize. . . .  107 
Platinotype,  Cold  Bath  Process  133 
Platinotype,  Hot  Bath  Process.  131 

Platinotype,  Negatives  for . 180 

Platinotype,  Solutions  for....  64 

Platinotype,  To  Print  on  the 

Paper . 131 

Platinotype  for  Permanence. . .  130 

Platinotype  Printing .  130 

Platinotype  Prints,  Clearing  . .  132 
Platinotype  Prints,  To  Develop  131 
Platinotype  Process  of  Printing 

Described .  131 

Pneumatic  Holders .  58 

Polariser .  35 

Polarizing  Apparatus  .  177 

Potassic  Carbonate,  Solution. .  62 
Potassic  Ferricyanide,  Reducer  63 

Potassic  Meta-bisulphite .  61 

Potassic  Oxalate,  Sat.  Solution  63 
Powell  and  Leland, Their  Micro¬ 
scopes .  24 

Powell  and  Leland’s  Apochro- 

matic  Condenser .  34 

“Power”..  . 31 


INDEX. 


PAGE 


Power  Depends  on  Focal 

Length .  31 

Preparations,  Bacteriological..  109 

Preparations,  Faded .  109 

Preparations,  Family  Red....  109 

Preparations,  Insect .  109 

Preparations,  Opaque  Yellow.  109 
Preparations,  Wanting  Con¬ 
trast  .  109 

Preparations  for  Work .  17 

Preserving  Sensitized  Albumen 

Paper .  117 

Presses  and  Shelves .  20 

Principles  For  Color-Correct 

Work  .  108 

Printing,  Principles  of .  115 

Printing  Frame,  To  Use . 117 

Printing  in  Platinum .  130 


Printing  on  Albumen  Paper. . .  115 
Printing  on  Albumen  Paper..  117 
Printing  on  Bromide  Paper. . . .  123 
Printing  on  Gelatine  Chloride.  121 
Printing  Processes,  Solutions 


for .  64 

Printing  Processes  in  General  111 

Prints,  To  Mount .  120 

Prisms  for  Monochromatic 

Light .  42 

Procedure  With  Easy  Objects. .  79 

Progressive  Examples .  79 

Projection,  Ocular,  To  Focus. .  85 

Projection  Oculars .  37 

Projection  Oculars . 164 

Projection  Oculars  by  Abbe 

and  Zeiss .  75 

Pyro,  for  Bromide  Paper . 128 

Pyro,  Solutions .  61 

Pyro-ammonia  Developer .  91 

Pyro-carbonate  Developer -  91 

Pyro  Developer  for  Wet  Collo¬ 
dion  .  147 

Quality  of  Gelatine  Plates. ...  65 

Quinol  Developer .  99 

Quinol  Developer  for  Bromide 

Paper .  128 

Quinol  Developer  For  Slides..  152 

Ramsden  Eye-Piece .  53 

Rapid  Emulsion,  Late  Advances 

in .  67 

Rapid  Exposure,  How  to  Make  54 

Rays,  Visual  and  Actinic .  27 

Reade,  Rev.  J.  B .  12 

Reds,  Plates  Sensitive  To .  107 

Reducing  Solution,  Farmer’s. .  63 

Reduction  of  Density . .  102 

Reduction  with  Iron  Chloride  63 
Reflections  in  Apparatus .  77 


•  • 
Yll 

PAGE 


“Register” .  53 

Removing  Hypo  from  Prints. . .  119 

“  Resolution  ”  Defined .  164 

Resolution  Increases  with  Ap¬ 
erture .  28 

Resolving  Power  in  Relation 

Aperture .  163 

Rigidity,  Essential  to  Micro¬ 
scope  .  22 

Ruby  Fabric .  55 

Ruby  Glass  for  Operating 

Room .  55 

Rose  Tap .  57 

Roux,  Dr.,  His  Magnesia 


S.  Gemma .  173 

“Safe”  Light  For  Operating 

Room . . .  56 

Safety  of  Light,  to  Test .  56 

Safety  Spring  for  Fine  Adjust¬ 
ment .  26 


Sciopticon  Lantern,  Scovill’s  . .  157 

Scovill’s  Optical  Lantern .  157 

Screen,  Aurantia,  To  Make..  108 

Screen,  Signal-Green . 108 

Screen  For  Optical  Lantern...  158 
Screens,  Use  of  With  Colors..  106 


Screens,  Worked  Glass .  108 

Screens  for  Orthochromatic, 
Must  Cut  Off  Violet  and 

Blue .  109 

Screens  for  Orthochromatic 


“Screens”  in  Color  Photog¬ 
raphy .  106 

Sections,  Thinness  of .  169 

Selection  of  Plates .  65 

Selenites  for  Polariser .  35 

Sensitizing  Albumen  Paper. . .  116 
Sensitising  Albumen  Paper, 

Bath  for .  64 

Sensitometer .  59 

Shadbolt,  his  Work .  15 

Shaw  Bull’s-Eye .  38 

Shutter  For  Exposing .  53 

Shutters  For  Lantern  Room. . .  159 

Side  Reflector  .  176 

Signal  Green  Screen  .  108 

Simple  Photo-Micro  Apparatus  47 

Sink  For  Operating  Room .  56 

Sinks,  India  Rubber .  57 

Sizes  of  plates .  52 

Slides  By  Contact,  To  Print. . .  145 

Slides  By  Reduction .  146 

Slides  By  Reduction,  Apparatus 

for...! .  146 

Slides  for  Optical  Lantern . 143 


vm 


INDEX. 


PAGE 


Slow  Development .  96 

Sodic  Carbonate,  Solution....  62 
Sodic  Hyposulphite,  Solution 

for  Fixing .  63 

Solution  for  Clearing  Negatives  63 
Solution  for  Reducing  Nega¬ 
tives .  63 

Solutions,  Carbonates  for  De¬ 
velopment .  .62 

Solutions  for  Photographic  Op¬ 
erations .  61 

Solutions  for  Platinotype .  64 

“Spot  Lens” . . 174 

Squeegee .  58 

Squeegee  for  Removing  Hypo 

from  Prints .  119 

Standard  Light  for  Bromide 

Printing... .  123 

Sternberg,  his  Work .  15 

Stock  of  Dry-Plates,  List  of. ..  68 

Stop  for  A.  Pellucida .  172 

Stopping  Down  Objective .  76 

Stops  for  Black  Grounds .  174 

Stops  in  Objectives .  76 

Strain  of  Objective .  75 

Stretch  Required  for  Camera. .  52 

Student’s  Stands .  26 

Subjects,  Difficult,  Treated  by 

Orthochromatics . . .  109 

Substage,  Importance  of .  22 

Substage  Condenser,  “  fitted  ”.  36 

Substage  Condenser,  Use  of. ..  69 

Substage  Condensers .  33 

Sulpho-pyrogallol,  Berkeley. .  61 

Sunlight,  Advantages  and  Dis¬ 
advantages  of .  18 

Sunlight,  Uncertainty  of .  39 

Sunlight  as  Radiant .  39 

Superiority  of  Apochromatics  85 

Surface  to  Focus  Upon .  52 

Swift  &  Son’s  Microscope _  24 

Swift’s  Multiplex  Condenser. . .  36 

Swift’s  Oil  Lamp .  45 

Swift’s  Photo- Micro  Apparatus  48 

Swift’s  Safety  Spring .  26 

Tables  of  Enlargement  and 

Reduction . 180,  181 

Tailfer  Patent,  The .  106 

Tanks  for  gases .  44 

Tanks  For  Gases .  161 

Temperature,  Equability  of  in 

Work-room .  19 

Test  Diatoms,  How  to  Treat. .  171 
Test  Diatoms,  Yellow  Mount¬ 
ing .  110 

Test  For  “  Safe”  Light .  56 

Test  Hairs,  To  Photo .  84 


tage 


Test  Objects,  Opticians’ .  31 

Testing  Lenses,  Advice  to 

Beginner  in .  32 

Tests  for  Objectives .  31 

Thickly-coated  Plates,  Use  of.  67 
To  Treat  Very  Opaque,  or  Non- 

Actinic  Subjects .  94 

Toning,  Rationale  of .  115 

Toning  Albumen  Paper .  118 

Toning  Bath  for  Albumen 

Paper .  118 

Toning  Bath  for  Aristotype 

Paper .  122 

Toning  Bath  for  Gelatine 

Chloride  Paper .  121 

Toning  Solutions  for  Albumen 

Paper .  64 

Toning  Wet  Collodion  Slides. .  149 

Transferotype  Paper .  127 

Truan  Y.  Luard,  Diatom  Pho¬ 
tos .  13 

Truan  &  Witt,  Their  Mirror .. .  40 

Tube  Correction. . . .  85 

Turmeric,  for  Screens .  109 

Under-exposure,  to  Rectify. .. .  97 

Uneven  Lighting . * . 104 

Varnishing  Negatives . 102 

Vertical  Illuminator,  Beck’s..  171 

Vibration,  Fatal  to  Success _  18 

Vibration,  to  Obviate  .  18 

Vignetting  Enlargements .  142 

Violent  Contrasts,  How  to 

Treat .  95 

Visual  and  Actinic  Rays .  40 

Vogel,  Color-Sen*jtive  Plates. .  106 
Walmsley,  Focusing  Surface. . .  53 

Washing  Albumen  Prints .  119 

Washing  Machines  for  Prints.  .  119 
Washing  Paper  Before  Toning  118 

Washing  Plates .  101 

Washing  Trough .  58 

Water  Supply.... .  20 

Water  Tap,  Adjuncts  to .  57 

Wave-lengths .  42 

Webster,  G.  W.,  Citrates .  98 

Wedgewood .  12 

Wellington,}.  B.,  His  Screen.  109 
Welsbach  Burner  as  Radiant. . .  39 

Wenham .  15 

Wenham’s  Parabolic  Illumin¬ 
ator .  175 

Wet  Collodion,  Chemicals  Re¬ 
quired  for .  60 

Wet  Collodion,  Fixing .  148 

Wet  Collodion,  Intensification  148 
Wet  Collodion,  Iron  Ammo- 
nio-sulphate  Developer .  148 


INDEX. 


IX 


PAGE 


Wet  Collodion,  Iron  Developer  148 
Wet  Collodion,  Pyro-developer  147 

Wet  Collodion  for  Slides .  144 

Wet  Collodion  Process .  146 

Wet  Collodion  Slides,  To  Tone  149 
White,  T.  Charters,  his  Work..  15 

Window  for  Dark-Room .  55 

Witt,  Otto  N.,  Diatom  Photos.  14 
Wood-Section,  Easy  Object. . .  79 

Woodward,  Dr.,  his  Work....  13 


PAGE 


Woodward’s  Camera  Described  40 
*’  Working  Distance  ”.  ..+...  30 

Yellow  Ground  on  Daitom 

Mounts .  110 

Zeiss,  Apalantic  Magnifier. ... .  53 

Zeiss,  Dr.  R.,  Photos  of  Dia¬ 
toms .  14 

Ziisonium  Oxide  to  Replace 
Lime .  45 


Description  of  Plates  after  Contents. 
F  rontispiece — 

Plate  I . 

Plate  II  . 

Plate  III . 

Plate  IV . 

Plate  V . 

Plate  VI . 


PAGE 

.Facing  46 
.Facing  79 
.Facing  104 
.  Facing  118 
.  Facing  136 
.Facing  152 


TMSGOVILL  &  ADAMS  COMPANY, 

Suoeessors  to  the  Photo  Department  ot  the 

SCOVILL  MANUFACTURING  COMPANY, 

(Established  in  1802.) 

4r23  Broome  Street,  1ST ew  ‘TxT ork : 

THE  LARGEST  MANUFACTURERS  OF 

Photographic  Cameras,  Apparatus 

and  Supplies 

IN  THE  WORLD,  FOR 

AMATEURS,  TOURISTS,  SCIENTISTS  AND 

PROFESSIONAL  PHOTOGRAPHERS. 

PHOTOGRAPHIC  LENSES  OF  ALL  KINDS. 

Flash  Light  Compound  for  Night  "Photography . 

jdll  the  Latest  Photographic  Novelties. 


PROPRIETORS  OF 

The  American  Optical  Co.’s  Factory. 

PROPRIETORS  OF  s 

New  Haven  Camera  Factory. 

PUBLISHERS  OF 

Scovill’s  Photographic  Series. 


W.  IRVING  ADAMS,  H.  LITTLEJOHN, 

President  and  Treasurer.  Secretary. 


THE 


No.  1  SCOVILL  SCIOPTICON, 
Complete  with  Double  Slide  Carrier, 

$30. 

No.  2  SCOVILL  SCIOPTICON, 
Complete  with  Double  Slide  Carrier, 

$50. 


After  experimenting  with  most  of  the  lanterns  in  the  market,  we  have 
come  to  the  conclusion  that  for  parlor  or  small  hall  exhibitions,  chemical 
and  optical  experiments,  etc.,  the  Scovill  Lantern  affords,  at  a  moderate 
price,  the  greatest  number  of  advantages,  and  from  its  simplicity  and  non¬ 
liability  to  get  out  of  order,  gives,  even  in  inexperienced  hands,  results 
superior  to  all  others. 

The  No.  1.  Scovill  Sciopticon  when  packed  for  carrying,  in  its  own 
Russia  iron  case,  measures  15  x  10  x  6  inches,  and  weighs  12  pounds;  the 
case  serving  as  a  convenient  stand  when  the  lantern  is  in  use. 

The  Case  and  Body  of  the  Lantern  are  of  Russia  iron,  and  neat  and 
compact  in  form.  That  part  of  the  body  which  surrounds  the  lamp  is  double, 
the  outer  covering  being  ornamentally  perforated  so  as  to  allow  a  constant 
current  of  air  to  circulate  and  keep  down  the  temperature. 

The  lamp  is  of  the  triple  wick  variety,  and  so  constructed  that  the  three 
flames  combine,  and  by  the  draught  of  a  ten-inch  chimney  give  a  brilliant 
flame. 

The  Condenser  is  four  inches  in  diameter,  neatly  mounted  in  brass, 
thoroughly  ventilated,  and  arranged  with  screw  flange  so  that  the  lenses 
may  be  separated  and  cleaned  when  required. 

The  Cone,  which  carries  the  objective,  and  the  mount  of  that  lens  are 
nickel-plated.  The  objective  is  a  double  achromatic  lens  of  one  and  a  half 
inch  clear  aperture  and  five-inch  focus,  so  that  at  a  distance  of  twelve  feet 
from  the  screen,  it  gives  a  brilliant  picture  on  disc  six  feet  in  diameter.  The 
focus  is  roughly  obtained  by  sliding  the  front,  carrying  both  cone  and  lens; 
and  fine  adjustment  by  a  rack  and  pinion  on  the  objective. 

The  No.  2  Scovill  Sciopticon  measures,  when  packed  in  case  for  car¬ 
rying,  18%  x  12  x  8%,  and  weighs  19  pounds.  The  objective  is  a  double 
achromatic  lens  of  1%  inches  clear  aperture  and  5%  inches  focus  so  that  at 
a  distance  of  about  twelve  feet  from  the  screen  it  shows  a  brilliant  picture 
on  disc  eight  feet  in  diameter.  The  lamp  has  five  wicks  and  is  corres¬ 
pondingly  more  powerful  than  the  lamp  with  the  No.  1  Sciopticon. 


THE  SCOVILL  &  ADAMS  COMPANY, 

423  Broome  Street,  New  York. 

ii 


THE  MERCER 


Bl 


16 


CAMERA. 


Size,  2fx3i.  Price,  $7.50. 


This  Camera  is  provided  with  a  Brass  Cone  and  Plate- 
holder  with  Ground  Glass  attached,  to  slide  back  and  fortn  in 
the  carriage,  as  desired. 


Mercer  Camera,  shown  with  Microscope  to  illustrate  working. 


iii 


THE  SCOVILL  OUTFIT 

For  PHOTOCRAPHINC  with  the  MICROSCOPE 


Photographing  with  the  microscope  has  hitherto  been  accomplished  by 
the  aid  of  elaborate  and  costly  apparatus,  and  been  applied  chiefly  to 
making  illustrations  for  scientific  magazines.  The  process  used,  that  of 
wet  collodion  in  connection  with  sunlight,  involved  the  procurement  of  an 
expensive  heliostat  to  produce  a  steady  illumination,  for  with  any  less 
powerful  light  the  exposure  would  necessarily  be  so  prolonged  that  the 
coating  of  the  plate  would  dry  and  become  useless.  Now  all  this  is 
changed,  for  with  the  modern  improvements  in  photography  which  are  the 
result  of  the  introduction  of  gelatine  dry  plates,  the  photographing  of 
microscopic  objects  becomes  as  easy  of  accomplishment  as  the  photograph¬ 
ing  of  the  beautiful  and  visible  in  nature  is  with  the  popular  amateur  outfits. 

The  scientist  and  microscopist,  instead  of  spending  hours  in  making 
imperfect  drawings,  aided  by  the  camera  lucida,  may  in  a  few  minutes,  with 
the  assistance  of  photography,  produce  a  more  perfect  representation  of  a 
minute  object  than  it  is  possible  for  the  hand  of  man  to  do,  working  con¬ 
jointly  with  the  eye.  Not  only  can  an  enlarged  image  of  a  microscopic 
object  be  formed  for  illustration,  but  professors  in  colleges  will  find  it  a 
ready  means  to  produce  negatives  of  a  suitable  size  from  which  may  be 
made  transparencies  or  magic  lantern  slides  for  exhibition  to  classes  or 
the  public. 


If  this  is  done  in  the  dayt^ntj.  a  room  from  which  all  white  light  is  ex¬ 
cluded  should  be  selected;  b  keepUsed  at  night,  as  in  most  cases  it  would 
be,  the  operations  may  all  be-ick  vnned  in  the  midst  of  a  family  group  for 
their  interest  and  amusemenirau^  to  impart  to  them  knowledge  of  the  mi¬ 
nute  life  or  organisms  of  the  .  .d  'which  the  microscope  alone  can  reveal. 


The  Scovill  Photomicroscopic  Equipment 


—  CONSISTS  OF  — 

1  Scovill  Special  Half  Plate  Camera. 

1  Multum  in  Parvo  Lantern,  with  Double  Condenser. 

1  dozen  4Kx5%  size  B  Keystone  Plates  to  make  Negatives;  also 
1  dozen  3 %  x  4M  size  A  Plates  for  Transparencies. 

Price,  Complete,  $18.00. 


The  presumption  is  that  you  are  provided  with  a  microscope.  If  not, 
we  recommend  the  purchase  of  one  from  a  regular  dealer  in  microscopical 
goods. 


Circular  containiag  directions  for  use  sent  with  each  outfit. 

iv 


THE  f  ALMSLEY  PHOTO-IICROGRAPHIC  CAMERA. 

Manufactured  by  the  American  Optical  Co*  Now  in  use  by 
many  Colleges  and  leading  Microscopists,  and  is  an  efficient,  practical 
and  cheap  instrument  for  the  purpose. 


It  is  made  in  two  forms:  the  cheaper,  No.  1,  (selling  for  $18.00)  is 
adapted  only  to  the  making  of  negatives  on  plates  334x434,  or  434x534»  as 
may  be  necessary.  The  complete  form  No.  2  (costing  $30)  is  also  a  minia¬ 
ture  enlarging,  reducing,  and  copying  camera,  admirably  adapted  to  the 
production  of  lantern  transparancies  from  any  size  negative  up  to  434x534* 

The  camera  (of  mahogany)  is  square,  carrying  a  Flammang  single 
plate  holder  for  434x534  plates  ;  usable  vertically  or  horizontally,  and  with 
kits  for  334x434  plates.  The  bellows  are  in  two  sections,  with  a  central 
division  of  mahogany,  which  carries  a  removable  partition,  to  which  a  suit¬ 
able  rectilinear  photographic  lens  can  be  attached,  for  enlarging,  reducing, 
or  copying.  A  light-tight  door  on  one  side  of  this  wooden  section  gives 
ready  access  to  the  lens  for  inserting  or  removing  diaphragms,  or  other 
necessary  manipulations,  whilst  a  milled  head,  accessible  from  the  same 

opening,  clamps  the  lens-bearing  section  firmly  to  the  bed  of  the  camera  at 

^  £ 

any  desired  point. 

The  bellows  have  an  extension  of  two  feet  in  addition  to  the  length  of 
the  box,  sliding  very  smoothly  upon  V-shaped  ways,  which  for  greater  con¬ 
venience  are  made  in  two  sections,  firmly  attached  to  each  other  by  wooden 
dowels,  and  a  solid  brass  screw,  worked  by  a  milled  head. 

The  bellows  are  firmly  held  at  any  desired  point  of  extension  by  a  cam, 
operated  by  a  lever  conveniently  placed  at  the  rear  of  the  focusing  screen 
which  latter  is  hinged  at  the  bottom,  and  when  not  in  use,  lies  out  of  the 
way  upon  the  extension  bed. 


v 


THE  SCOV1LL 


CAMERAS. 


When  ordering,  please  specify  number  and  sizes 
of  kits,  also  style  of  Holder  wanted. 


No.  61.  Size, 

(>y2 

X 

%l/2 

Price, 

$30.00 

No.  62. 

8 

X 

10 

a 

• 

35-oo 

No.  63. 

IO 

X 

12 

44 

• 

48.00 

N  0.  64. 

I  I 

X 

14 

i  4 

• 

60.00 

No.  65. 

14 

X 

17 

a 

• 

72.00 

No.  66. 

17 

X 

20 

a 

• 

90.00 

No.  66*^.  “ 

18 

X 

22 

44 

• 

100.00 

No.  67.  “ 

20 

X 

24 

44 

9 

1 10.00 

Special  sizes  and  styles  made  to  order. 


VI 


FEW  SETS  LEFT 


The  American  Annual  of  Photography 
1  Photographic  Times  Almanac  for  1887 

(SECOND  EDITION.) 

Contains  five  full-page  illustrations— 

Am  Exquisite  Photo-Gravure,  by  Ernest  Edwards. 

A  Bromide  r*riiit,  by  the  Eastman  Company. 

A  Silver  Print,  by  Gustav  Cramer,  of  St.  Louis. 

Two  Mosstypes,  by  the  Moss  Engraving  Company. 

197  pages  of  Contributed  Matter  consisting  of  articles  on  various  subjects,  by  80  repre¬ 
sentative  photographic  writers  of  this  country  and  Europe. 


The  American  Annual  of  Photography 
1  Photographic  Times  Almanac  for  1888 

Contains  eight  (8)  full-page  high-grade  illustrations  ;  and  over  ninety  (90)  original  con¬ 
tributions,  written  expressly  for  its  pages,  by  the  most  eminent 
photographic  writers  of  Europe  and  America. 

THE  ILLUSTRATIONS  COMPRISE: 

A  Photo-Eithog:r»ph.  showing  an  improved  new  process,  by  the  Photo 
Gravure  Company  of  New  York. 

A  Photo-Copper-Plate  Engraving  of  a  Pictorial  Landscape  Subject, 
by  E.  Obemetter,  of  Munich. 

A  Melsenbach  of  “The  Old  Stone  Bridge,”  by  Kurtz. 

A  25 inc  Etching,  from  the  Engraving,  which  is  itself  as  fine  as  an  Engraving, 
by  Stevens  &  Morris. 

A  Charming  Child  Portrait,  by  Crosscup  &  West’s  improved  process. 

-<  Three  Mosstypes  of  popular  subjects.  And 

330  PAGES  OF  VALUABLE  INFORMATION. 


The  American  Annual  of  Photography 
1  Photographic  Times  Almanac  for  1889 

Surpasses  Even  Its  Two  Predecessors. 

The  full-page  pictorial  illustrations  are  more  numerous  and  superior  in  quality  than 
have  ever  before  been  presented  in  any  Photographic  Annual,  and  the  reading-matter 
is  in  accord  with  the  high  standard  of  the  illustrations. 

The  full-page  pictures  are  as  follows : 

A  Charming  Portrait  of  the  Beautiful  Eilllan  Russell,  from  a 
negative  by  Falk,  printed  on  the  new  American  Aristotype  Paper. 

'Watering:  His  Horse.  A  Characteristic  Group,  by  Geo.  B.  Wood,  of  Phila¬ 
delphia,  printed  in  Highest  Grade  Photo-Gravure,  by  the  Photo-Gravure  Company 
New  York. 

Yes’m,  I’m  Coming:.  A  Picture  of  the  Small  Boy.  By  Mr.  F.  Gutekunst,  of 
Philadelphia,  in  his  exquisite  manner  of  Mechanical  Printing. 

The  Arab  Sheik.  A  Study  of  Orthochromatic  Photography,  by  William  Kurtz, 
printed  by  the  Meisenbach  Process. 

A  Scene  in  the  Tyrolese  Alps.  From  an  Original  Photograph  by  Charles 
Scolik.  By  the  Crosscup  &  West  Engraving  Company. 

The  Divers.  An  Instantaneous  Study  on  a  Carbutt  Plate,  reproduced  in  Meisen¬ 
bach. 

After  the  Theatre.  A  Magnesium -light  Photograph  by  Mons.  Flammang. 

By  Photo-Electro  Engraving  Company. 

By  the  Sea.  An  Eastman  Bromide  Picture.  By  E.  W.  Newcomb. 

Three  Mosstypes. 

Paper  Coverg,  (By  mail,  12  cents  extra.)  $0  SO 

Library  Edition,  “  ■  ■  •  J 

Edition  de  Luxe,  (postpaid)  -  2  50 

THE  SCOVILL  &  ADAMS  COMPANY,  Publishers. 


vii 


- ►  TIITC  ♦— - 

^merieap  pijpual  of  P^oto^rapfyy 

Hi  P^oto^raptyis  Ji/T\es  ^Imapao 

— -* - For  1890. — *♦• — ^ 

(FIFTEENTH  THOUSAND.) 


LIST  OF  FULL-PAGE  PICTORIAL  PLATES. 

“ Thomas  Edison;**  A  Portrait  of  the  Eminent  Electrician.  George 
M-  Allen  &  Co.,  New  York. 

“  Babyhood  ;**  A  Tinted  Photo-Gravure.  The  Photo-Gravure  Company  of 
New  York. 

“  Putnam’s  Escape  ;**  A  Collection  of  Historic  Views.  The  Crosscup 
&  West  Engraving  Company,  Philadelphia. 

“  Southern  Fruit  ;*’  An  Orthochromatic  Study.  The  Electro-Light 
Engraving  Company,  New  York. 

“At  the  Barracks  ;’*  A  copy  of  the  great  Meissonier  picture.  William 
Kurtz,  New  York. 

“  Minstrel  Party  at  *  John  Brown’s  Fort.”*  Photo-Engraving  Co., 
New  York. 

“John  Brown’s  Home  and  Grave.”  Lewis  Engraving  Company, 
Boston. 

“Off  Duty;”  An  Instantaneous  Study.  William  Kurtz,  New  York. 

“  Minnehaha  Falls  in  Winter.”  Levytype  Company,  Philadelphia. 
“  Central  Park;”  In  the  Menagerie.  I.  M.  Van  Ness,  New  York. 

“A  Merry  Tale;”  A  Child  Group.  F.  Gutekunst,  Philadelphia. 
u  The  Van  Rensselaer  Manor  House.”  Photo-Electro  Engraving  Co., 
New  York. 

“  An  Improvised  Studio.”  Electro-Tint  Engraving  Company,  Phila¬ 
delphia. 

“The  Bats;”  A  “Flash”  Light  Photograph  in  Howe’s  Cave.  William 
Kurtz,  N.  Y. 

“A  Raider’s  Resort;”  Morgan’s  Favorite  Rendezvous.  M.  Wolfe, 
Dayton,  Ohio. 

“Group  of  Esquimaux.”  William  Kurtz,  New  York. 

“Diatoms;”  Photo-Micrographs.  William  Kurtz,  New  York. 

“  Tropical  Luxuriance  ;”  A  Scene  in  Florida.  Moss  Engraving  Co., 
New  York. 

“An  Arctic  Camp.”  Moss  Engraving  Company,  New  York. 

“Home  of  Edgar  Allan  Poe.”  Moss  Engraving  Company,  New  York. 

From  the  above  list  ot  full-page  pictorial  plates,  it  will  be  seen 
that  The  American  Annual  of  Photography  and  Photographic 
Times  Almanac  for  1890,  in  point  of  pictures,  will  command  widespread 
popularity  !  Twenty  full-page  pictorial  plates  is  an  unprecedented  number 
of  illustrations  for  such  a  publication.  They  show  the  progress  which 
has  been  made  in  photographic  illustration,  being  excellent  examples 
of  the  latest  improvements  in  photographic  printing,  and  represent  more 
than  twelve  distinct  processes  of  photo-mechanical  reproduction. 

Price,  fifty  cent*  in  paper  (by  mail,  fourteen  cents);  library  edition,  one  dollar. 

With  the  PHOTOGRAPHIC  TIMES  (weekly,  illustruted  edition), 

$5.50,  post  paid.  Edition  de  Luxe,  per  copy,  $5.00. 

THE  SCOVILL  &  ADAMS  COMPANY,  Publishers. 


Vlll 


“The  Processes  of  Pure  Photography.” 


(Number  Twenty-nine  of  The  Scovill  Photographic  Series.) 

+ - by - + 

W.  K.  BURTON,  C.E.,  and  ANDREW  PRINGLE, 

Professor  of  Sanitary  Engineering  Imper-  President  of  the  Photographic  Convention 
ial  University  of  Japan,  Author  of  of  the  United  Kingdom,  1889,  Fellow 

“  Modern  Photography,”  “Photo-  of  the  Royal  Microscopical 

graphic  Printing,  Etc.  Society,  Etc. 


Of  the  two  writers,  both  have  zealously  followed  photography  as  something  more 
than  a  mere  amusement,  for  a  considerable  number  of  years.  One  of  the  writers  has 
studied  the  science  from  a  theoretical  and  experimental  point,  while  the  other  writer’s 
attention  has  been  almost  entirely  directed  to  the  production  of  practical  results  by  the 
processes  known,  and  by  each  process  as  it  has  been  given  to  the  world.  As  the  joint 
work  of  two  acknowledged  authorities  in  photography,  and  as  every  word  in  it  refers  to 
subjects  with  which  the  authors  are  personally  and  intimately  acquainted— with  not  a 
direction  or  a  formula  given  on  trust—”  The  Processes  of  Pure  Photography  ”  possesses 
a  practical  value  that  justly  entitles  it  to  become  at  once 

A  STANDARD  WORK. 

It  not  only  contains  the  best  of  all  the  processes  and  methods  which  have  been  tried 
by  the  experienced  authors,  but  also  includes  much  that  is  new  and  has 

NEVER  BEFORE  BEEN  PUBLISHED. 


FOLLOWING  IS  THE 

CONTENTS  OF  THIS  COMPLETE  BOOK 


Chapter. 

I. — Introductory  and  Historical. 

II. — The  Theory  of  Photography. 

III. — Apparatus. 

IV.  — The  Dark-room. 

V. — “Negative”  and  “Positive.” 

VI. — The  Wet  Collodion  Process. 

VII. — A  Dry  Collodion  Process. 

VIII. — Gelatine  Emulsion  Processes,  Pre¬ 
liminary. 

IX. — Gelatine-bromide  Emulsion. 

X.— Gelatine-bromide  Emulsion, by  the 
Ammonio-nitrate  Process,  and 
Precipitation  by  Alcohol. — Cen¬ 
trifugal  Separation. 

XI. — Coating  Plates  with  Gelatine-bro¬ 
mide  Emulsion,  Drying,  Etc. 

XII./— The  Camera  in  the  Field. 

XIII.  — Exposure  and  Development  Gen¬ 

erally  Treated. 

XIV. — Development  of  Gelatine-bromide 

Plates. 

XV. — Gelatine-bromide  Plates— Fixing, 
Intensification,  Reduction,  Etc. 

XVI. — Defects  in  Gelatine-bromide  Nega¬ 
tives. 


Chapter. 

XVII.— Paper  Negatives  and  Stripping 
Films. 

XVIII.— “  Color  Correct,”  or  “  Ortho- 
chromatic  Photography. 

XIX.— Stereoscopic  Photography. 

XX. — Part  II.  Printing  Processes, 

Preliminary. 

XXI. — Printing  on  Albumenized  Paper 
with  Silver  Chloride. 

XXII.— Preparation  of  Negatives  for 
Printing,  Combination  Print¬ 
ing,  Vignetting. 

XXIII.— Printing  on  Plain  Salted  Paper. 

XXI V.— Gelatine-chloride  Paper  for 
Printing-out. 

XXV.— Contact  Printing  on  Gelatine- 
bromide  Paper. 

XXVI. — Rapid  Printing  Paper. 

XXVII.— Platinotype,  or  Printing  in  Pla¬ 
tinum. 

XXVIII. — The  “Carbon  Process,”  or 
“  Pigment  Printing.” 

XXIX.— Positives  and  Negatives  by 
Enlargements. 

XXX.— Lantern-slides. 

XXXI. — Residues. 


Price,  in  paper  covers . $2.00  |  Library  Edition .  $2.50 

THE  SCOVILL  &  ADAMS  COMPANY,  Publishers. 

ix 


THE 


OPTIQIfc  MNTERN 

FOR 


Instruction  and  Amusement. 


BY 


ANDREW  PRINGLE,  F.R.M.S., 


President  Photographic  Convention  of  the  United  Kingdom,  i88q. 


FULLY  ILLUSTRATED. 


LANTERN  SLIDE  MAKING.  By  the  same  Author.  In  Preparation. 


THE  SCOVILL  &  ADAMS  COMPANY,  Publishers. 


The  Photographic  Instructor. 

FOR  THE  PROFESSIONAL  AND  AMATEUR. 


(Number  Twenty-six  of  The  Scovill  Photographic  Series.) 


ScLited  Toy  "W".  X.  Lincoln  i^.dam.8, 

With  an  Appendix  by  Prof.  Charles  Ehrmann. 

The  most  thoroughly  practical  instruction  book  yet  published  and  the 
most  complete,  consisting,  as  it  does,  of  the  Comprehensive  Series  of 
Practical  Lessons  issyed  to  the  students  of  the  Chautauqua  School  of 
Photography,  revised  and  enlarged,  with  an  Appendix  of  over  thirty  pages, 
on  the  Nature  and  Use  of  the  Various  Chemicals  and  Substances  Employed 
in  Photographic  Practice,  besides  valuable  Tables  of  References,  etc. 

The  original  Lessons  were  contributed  by  such  competent  photographic 
writers  as 

Charles  Wager  Hull,  Superintendent  of  the  Chautauqua  School  of  Photog¬ 
raphy  ;  Prof.  Randall  Spaulding,  Superintendent  of  the  Montclair 

Public  Schools ;  Prof.  Karl  Klauser,  of  Farmington,  Cotin.  ; 

Dr.  Maurice  N.  Miller,  of  the  University  of  the  City  of  New 
York  ;  John  Carbutt,  the  well-known  Dry -plate  Manufac¬ 
turer  of  Philadelphia ;  O.  G.  Mason,  of  Bellevue 
Hospital,  New  York  City;  Prof.  Chas.  Ehrmann, 

Instructor  of  the  Chautauqua  School  of  Photog- 
graphy ;  and  W.  I.  Lincoln  Adams, 

Editor  of  the  Photographic  Times. 

Each  being  an  authority  on  the  subject  of  which  he  treats. 

The  Appendix  is  a  complete  chemistry  of  reference  in  itself,  and  is 
invaluable  to  every  photographic  worker. 


A  glance  at  the  complete  Table  of  Contents  show  the  scope  of  the  book  : 


Lessons. 

Preface. 

Introduction. 

I.  Apparatus. 

II.  Management  of  Apparatus  in  the 
Field. 

III.  The  Dark-room. 

IV.  Exposing. 

V.  Developing. 

VI.  Fixing,  Washing,  Varnishing,  In¬ 
tensifying,  and  Reducing. 

VII.  Printing  on  Albumenized  Paper. 

VIII.  Printing  on  Various  Other  Papers. 

IX.  Printing  on  Permanent  Bromide 
Paper. 

X.  Artistic  Printing. 

XI.  T rimming  and  Moun  ting  the  Prin  ts . 

XII.  Spotting  and  Burnishing  the  Prints. 

XIII.  Portraiture. 

XIV.  Retouching  the  Negative. 


Lessons. 

XV.  Photographing  Interiors  and  In¬ 
animate  Objects. 

XVI.  Copying,  Enlarging,  and  Reduc¬ 
ing. 

XVII.  Orthochromatic, or  Color-sensitive 
Photography. 

XVIII.  Transparencies,  andjHow  to  Make 
Them. 

XIX.  Landscape  Photography. 

XX.  Stereoscopic  Photography. 

XXI.  Light  and  Lenses. 

XXII.  Photo-micrography. 

XXIII.  Photographing  by  Artificial  Light. 

XXIV.  Emulsion  Making. 

Appendix  on  the  Nature  and  Use 
of  the  Various  Chemicals  and 
Substances  Employed  in  Photo¬ 
graphic  Practice. 


The  book  is  embellished  with  Five  Full-page  Pictorial  Illustrations ,  besides  numer¬ 
ous  Cuts,  Diagrams,  etc.,  illustrating  the  letter-press. 

Two  hundred  pages  of  valuable  Reading  Matter. 


Price,  in  illuminated  paper  covers,  ...  $0  75 

Price,  library  edition,  uniform  with  other  numbers 

of  the  series,  -  -  -  -  -  125 

For  sale  by  all  dealers  in  photographic  goods,  or  sent  by  mail,  post-paid,  on 
receipt  of  price,  by  the  publishers, 

THE  SCOVILL  &  ADAMS  COMPANY. 


XI 


“Bi^y  Plate  Makir© 

[NO.  20  OF  THE  SCOVILL  PHOTOGRAPHIC  SERIES]. 

By  GEO.  L.  SINCLAIR,  M.D. 

Reprinted,  from,  “The  Photogrphlc Times with  additions  and  corrections. 
Edited  by  W.  I.  Lincoln  Adams. 


A  SERIES  OF  PRACTICAL  ARTICLES  ON 

•Artjafeui*  Brr)ulsi®i)  Simple  ^  ctppaiii®!)  af  ll )® 

Jfpeiciical  Experiejgee  ®  f  ®p. 


THE  EMULSION, 

WASHING, 

MELTING, 

A  RAPID  EMULSION, 


IT  TREA  TS  OF - 

GELATINE, 

PREPARING  THE  GLASS 
FOR  COATING, 

COATING.  Etc.,  Etc. 


Royal  octavo,  leatherette  binding . 50c. 


By  E.  J.  WALL, 


AN  AUTHORIZED  AMERICAN  EDITION. 

As  a  reference  book  and  photographic  cyclopedia  it  is  invaluable  to 
every  photographer,  be  he  professional  or  amateur.  Concise  definitions  of 
all  terms  used  in  photography  are  given  in  such  a  manner  that  they  may 
be  easily  and  quickly  found.  The  book  is  printed  on  fine  supersized  and 
calendered  paper,  and  bound  substantially  and  neatly  in  cloth,  uniform 
with  the  other  volumes  of  The  Scovill  Photographic  Series.  It  con¬ 
sists  of  240  pages,  royal  octavo. 

Price  Only  $1.50. 

Each  book  enclosed  in  a  neat  paper  mailing  case. 


THE  SCOVILL  &  ADAMS  COMPANY,  Pablishers, 

xii 


Photographic  Publications. 

(Selected  from  the  Scovill  Catalogue  of  Books.) 

Price, 
Per  Copy. 

THE  KNACK .  $o  40 

THE  CHEMISTRY  OF  PHOTOGRAPHY.— By  Prof.  Raphael  Meldola. 

Cloth  bound .  2  00 

THE  FERROTYPERS’  GUIDE. — Cheap  and  complete.  For  the  ferrotyper,  this 

is  the  only  standard  work.  Seventh  thousand .  75 

THE  PHOTOGRAPHERS’  BOOK  OF  PRACTICAL  FORMUL^E.-Compiled 

by  Dr.  W.  D.  Holmes,  Ph.B.,  and  E.  P.  Griswold.  Paper  covers .  75 

Cloth  bound .  1  50 

THE  PHOTOGRAPHIC  STUDIOS  OF  EUROPE.— By  ,H.  Baden  Pritchard, 

F.C.S.  Paper .  50 

Cloth .  1  00 

ART  OF  MAKING  PORTRAITS  IN  CRAYON  ON  SOLAR  ENLARGE¬ 
MENTS.  (Second  Edition).  By  E.  Long.  Price .  50 

PHOTOGRAPHY  APPLIED  TO  SURVEYING.  Illustrated.  By  Lieut.  Henry 

A.  Reed,  U.S.A.  Cloth  bound . 2  50 

HISTORY  AND  HAND-BOOK  OF  PHOTOGRAPHY.— Translated  from  the 

French  of  Gaston  Tissandier,  with  seventy  illustrations.  Cloth  bound,  reduced  to  75 

A  COMPLETE  TREATISE  ON  SOLAR  CRAYON  PORTRAITS  AND 
TRANSPARENT  LIQUID  WATER-COLORS.— By  J.  A.  Barhydt.  Practical 
ideas  and  directions  given.  Amateurs  will  learn  ideas  of  color  from  this  book 
that  will  be  of  value  to  them.  And  any  one  by  carefully  following  the  directions 
on  Crayon,  will  be  able  to  make  a  good  Crayon  Portrait .  50 

ART  RECREATIONS. — A  guide  to  decorative  art.  Ladies’  popular  guide  in  home 

decorative  work.  Edited  by  Marion  Kemble .  1  50 

PADDLE  AND  PORTAGE. — By  Thomas  Sedgwick  Steele.  Illustraied .  1  50 

AMERICAN  CARBON  MANUAL. — For  those  who  want  to  try  the  carbon  print¬ 
ing  process,  this  work  gives  the  most  detailed  information.  Cloth  bound .  1  00 

MANUAL  DE  FOTOGRAFIA.— By  Augustus  Le  Plongeon.  (Hand-Book  for 

Spanish  Photographers.) .  1  00 

SECRETS  OF  THE  DARK  CHAMBER.—  By  D.  D.  T.  Davie .  50 

AMERICAN  HAND-BOOK  OF  THE  DAGUERREOTYPE.— By  S.  D.  Hum¬ 
phrey.  (Fifth  Edition.)  This  book  contains  the  various  processes  employed  in 
taking  Heliographic  impressions.  Reduced  to .  10 

THE  PRACTICAL  PHOTOGRAPHIC  ALMANAC .  25 

MOSAICS  FOR  1870, 1871,  1872,  1873,  1875,  1882, 1885, 1886, 1887, 1888, 1889, 1890 .  25 

BRITISH  JOURNAL  ALMANAC  FOR  1878,  1883,  1887 .  25 

PHOTO.  NEWS  YEAR-BOOK  OF  PHOTOGRAPHY  FOR;i87o,  1871,  1887, 1888  25 

THE  PHOTOGRAPHER’S  FRIEND  ALMANAC .  25 

AMERICAN  ALMANAC  OF  PHOTOGRAPHY .  25 

PHOTO.  NEWS  YEAR  BOOK  OF  PHOTOGRAPHY  for  1890 .  So 

WALDACK’S  PHOTO.  ALMANAC .  25 

xiii 


WILSON’S 


WILSON’S  QUARTER  CENTURY  IN  PHOTOGRAPHY.  By 
Edward  L.  Wilson,  Ph.D.  “The  best  of  everything  boiled 
out  from  all  sources.”  Profusely  illustrated,  and  with  notes 
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WILSON’S  PHOTOGRAPHICS.— “Chautauqua  Edition,”  with 
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pages.  Finely  illustrated .  4  f0 


BURNET’S  ESSAYS  ON  ART.  A  facsimile  reproduction  of  the 
costly  original  edition,  Will  help  every  portrait  maker,  every 
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PHOTO-ENGRAVING,  PHOTO-ETCHING,  AND  PHOTO¬ 
LITHOGRAPHY.  By  W.  T.  Wilkinson.  Revised  and  en¬ 


larged  by  Edward  L.  Wilson,  Ph.D.  Illustrated.  180  pages, 

all  new.  Only  American  edition,  Cloth  bound .  3  00 

WILSON’S  PHOTOGRAPHIC  MAGAZINE.  Edited  by  Ed¬ 
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VOGEL’S  PROGRESS  IN  PHOTOGRAPHY.  By  Dr.  H.  W. 

Vogel.  Illustrated .  .  3  00 

THE  BOOK  OF  THE  LANTERN.  By  T.  C.  Hepworth,  Editor 
of  the  (London)  Amateur  Photographer.  A  complete  manual  for 
the  Lanternist  and  Slide  Maker.  278  pages .  2  00 


THE  PHOTOGRAPHIC  COLORISTS’  GUIDE.  By  John  L. 

Gihon.  The  newest  and  best  work  on  painting  photographs. . .  1  50 

PHOTOGRAPHIC  MOSAICS,  1890.  An  annual  record  of  photo¬ 
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W'  SEND  FOR  CATALOGUE!  OF  PARTICULARS. 


EDMHRD  L-.  MIL-SON, 

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xiv 


Edited  by  W.  I.  LINCOLN  ADAMS. 

IS  ILLUSTRATED  EVERY  WEEK 

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P.  C.  DUCHOCHOIS,  on  Chemical  Subjects. 

W.  J.  STILLMAN,  on  Art  and  Practical  Sub¬ 
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Webster,  F.C.S.,  of  England;  CarlSrna,  Charles 
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Volkmer,  of  Austria;  Dr.  Lohse,  Dr.  Schnauss, 
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The  Chemistry  of  Photography,  by  W.  Jerome 
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Notes  and  News, 

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XV 


Trade  Mark. 


“  ECLIPSE,”  Sen.  27. — Films  and  plates  are  extremely  sensitive,  and 
specially  intended  for  quick  studio  exposures,  concealed  and  detective 
cameras,  instantaneous  views,  and  magnesium  flash-light  photography. 

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values.  The  best  plates  for  landscapes,  interiors,  and  photo-microg¬ 
raphy. 

“A”  GELATINO-ALBUMEN  Plates. — For  lantern-slides  and  window 
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PROCESS  PLATE. — For  use  by  photo-lithographers,  photo-engravers, 
and  zinc-etchers  in  making  intense  and  clear-line  negatives.  Sen.  12. 

CARBUTTS 

LANTERN  TRANSPARENCY  PLATES 

Yield  beautiful  results  with  HYDRO,  or  EIKO.  Developer. 

CARBUTT’S 

Flexible  “Celluloid”  Films. 

NEGATIVE  AND  POSITIVE. 

THE  PERFECTION  OF  FILM  PHOTOGRAPHY. 

Bulk  and  Weight  Reduced  to  a  Minimum. 

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• 

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Order  through.  Your  Dealer. 

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PRICE  LISTS  SENT  ON  APPLICATION. 


MANUFACTURED  BY 

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Bausch  &  Lomb  Optical  Co. 

MANUFACTURERS  OF 

Microscopes, 

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Photographic  Lenses 

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PHOTO-MICROGRAPHIC  1 

CAMERAS. 

Made  in  three  different  Forms ,  adapted  to  all  modern 

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P.  O.  Drawer  29a. 


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p.  O.  Box  433. 


Illustrated  Catalogue  sent  on  application  free  to  any  address. 


XVII 


4 


l 


1 


I 


GETTY  CENTER  LIBRARY  CONS 

QH  251  P95  1890  BKS 

c.  1  Pringle.  Andre* 


Practical  photo-micrography  :  by  the  lat 


3  3125  00257  2374 


1 


V  . 


